How Coffee Varietals and Processing Affect Taste

I recently read James Hoffman’s fantastic book The World Atlas of Coffee and followed the also fantastic new Terroir course at the Barista Hustle web site. All of this reading motivated me to think a bit more about coffee varietals when I’m enjoying a cup of coffee. Previously, I had noticed some obvious taste differences between varietals, like the fact that typical Kenyans such as the SL28 varietal tend to have a nice taste of blackberries (or tomato when the roast is underdeveloped) but I did not think about it much further.

His book also made me realize that I couldn’t find much information about the typical taste profiles of different coffee varietals or processing methods, other than anecdotic facts and tasting notes of individual roast batches. Clearly, there is a ton of subjective tasting notes available out there, and I thought if we could only collate a big pile of them, I could probably distill it and see if some interesting trends come out of that.

I decided to contact Alex, a friend who built a really cool mobile application (for iOS and Android) called Firstbloom, where they actually did just that. They allow users to build their own personal library of various roaster’s bags and consult other people’s ratings. One really nice thing about it is that unavailable past offerings don’t disappear (some day, someone will need to explain to me why roasters always completely delete web pages of their past offerings, rather than just unlink them). Anyway, Alex was super happy to help me with this idea, and he generously sent me his metadata on 1,500 coffee bags with varietals, tasting notes and processing for every one of them ! Alex and his team built Firstbloom as a passion project (much like my blog), and I’m highly appreciative of their work and precious help with this idea. So, in a way, today’s blog post was sponsored by Firstbloom’s incredible efforts at collating these data, otherwise it would not have been possible.

Taste Descriptors by Coffee Varietal

The first thing I decided to investigate is the taste descriptors that come up most often for each coffee varietal. For this I only used coffee processed with the washing method, because it is the most abundant and I also think it is the process that will bring up varietal characteristics most clearly without influencing them (don’t tell Scott Rao, but there are some naturals that I love even if I think they distort the tasting profile). A very neat tool to visualize such data is a word cloud; each word is displayed with a size representative of how often it came up in a list. There are some Python packages that do basic word clouds, but I found out this website that offers way more options. Coding that from scratch seemed like an annoying enterprise, so I decided to just use it.

I did not just collate all of the taste descriptors and count the number of repetitions when I assigned weights to each word, the way one would typically build a word cloud. This would be an ok way to do things, but it would not necessarily amplify the differences from one varietal to the other. As you can see in that figure, there are some words that come up way more often than others when describing any kind of coffee:

These descriptors are not the most interesting to me, as they are the ones that come up most often regardless of varietal. What I would rather want to see are the specific descriptors that come out in one varietal more than in others. To do this, I counted the number of times a descriptor happened within a varietal, and normalize that to the amount of times it happened in any coffee, hence the descriptors in larger fonts above will be somewhat muted. In other words, if a taste descriptor happens a lot for SL28 and not that much for other varietals, it will be amplified more than a descriptor that happens a lot for SL28 as well as any other coffee. There is one potential drawback of doing this: Imagine there is just one bag of coffee ever that had the taste descriptor carrot. It would end up being extremely amplified in the word cloud of the one varietal where it happened, because it was never used for any other coffee. To mitigate that effect, I put a “ceiling” on the level of amplification that rare words can obtain; I decided that no word could be amplified by a factor larger than 3.3 because of its rare use in other coffee varietals.

Now, the fun part ! Here are some collections of taste descriptors for some of the most widespread coffee varietals:

This already jumped out as very representative of my experience. Ethiopian heirloom coffees often taste very floral and have a distinct citrus-like character often described as lime (see this great book review by James Hoffman where he talks a bit more about “heirlooms”). As I expected, SL28 is largely dominated by descriptors like blackberries or black currant. Just writing this makes me want to brew a good Kenyan cup. The Geisha varietal seems dominated by floral and fruity descriptives, my personal favorites (I’m so original). One thing that surprised me a bit more is how Caturra and Bourbon come out quite similar. But this is not actually that surprising, because Caturra arose from a naturally occurring mutation of the Bourbon varietal (as described at World Coffee Research).

There are some significant caveats I should add to these results. First, there are some taste descriptors that are caused by roasting more than varietal. I suspect that some varietals like Caturra are a bit harder to roast properly, and to diagnose once they are roasted compared to most Kenyan and Ethiopian coffees. If I’m right about this, then there will be some part of the unique characters of Caturra above that might be caused by a less optimal average roasting, and not by genes. For example, I suspect that some nutty descriptors might be part of that category.

Another likely bias comes from terroir, which might have a strong effect on taste; by terroir, I refer to the type of soil, weather, shade and other aspects of how farmers take care of their crops. Add this to the fact that some countries like Kenya often grow a very selective list of varietals (e.g. SL28, SL34, Batian and Ruiru 11), you will end up with a strong varietal versus terroir correlation. This means that some of the taste descriptors coming up in SL28 above could have more to do with terroir than actual coffee genes. In order to tell them apart, we would need a lot more data on typical Kenyan crops grown outside of Kenya. If we look at the word clouds of these four particular species next to one another, it might make you worry even more about this strong correlation:

These four varietals are also sometimes grown, roasted and sold as a blend , so the taste descriptors for the three species will also tend to be somewhat mixed together, even in the unlikely scenario where there was no effect from terroir.

Although these word clouds are biased by terroir and roasting, they are still super useful to me, because the bags of coffee that I’m gonna drink are also affected by the same biases. From a user perspective, it’s therefore really fun to know which varietals will typically get you in what kind of taste territories. I would however bet that in 10 years, a typical user experience might shift far from the word clouds above.

But even this more limited use of the word clouds above is not perfect, because there’s yet another effect that clearly taints these word clouds, and will make them a little bit less reliable as a guide to which coffee you want to buy: human bias. I found that roasters will very rarely write tomato on their bag of Kenyan coffee, even when it tastes like nothing else but tomato soup. This is not surprising, because tomato it is widely known as a roast defect form under-developed Kenyan coffee, so it would be a bit of a bad self publicity to write that on a bag of coffee. Therefore, there are some “surprise” taste descriptors that won’t end up in the word clouds above, but may end up in your cup of coffee !

Taste Descriptors by Coffee Processing

Another aspect that is widely known to affect the taste profile of a cup of coffee is the process by which the pulp is removed and the coffee beans are dried, generally referred to with the umbrella term processing. So, I decided to make similar charts, but this time grouping bags by processing rather than varietal. This is what came up for the two most dominant processing methods, washed versus natural:

Hahaha, that was just a joke ! Here’s what really came up from the actual data on natural-processed coffees:

I may be joking about it, but there are a lot of naturals that don’t actually taste dirty at all. I enjoy these “clean” naturals much more than the other ones, but that’s just my preference. For example, all natural coffees I ordered from Gardelli yet were very clean, and I loved them.

The same limitations that I mentioned above still apply here, plus a new one: some varietals tend to never be natural-processed (e.g. the typical Kenyan varietals) or vice-versa, and that will introduce some correlation between varietal and processing, further biasing the two word clouds above. I remember reading that the way “washed” coffees are processed in Kenya versus Colombia is also very different, so that’s yet another bias !

Speaking of human biases, here’s a really funny observation:

One of the top descriptors of honey-processed coffee is honey… hmmmm suuure, I’m very skeptical that this is not just tasters influenced by the actual process name. I would bet a full dollar that other descriptives in the sweet category might replace it if we did this blindly.

While I showed you the word clouds for the main categories, I generated a lot more of them. I will all gather them at the end of this post so that it doesn’t get too cluttered with figures !

The Flavor Wheel

So, that was super interesting to me, but there are more fun things we can do. For example, a few groups have defined flavor wheels for visualizing coffee flavors; those of the Specialty Coffee Association (SCA) and Counter Culture are probably the most well-known, but I thought there would be a way to arrange categories and the wheel itself in a way that would be more intuitive to me; here’s how I defined the first- and second-level categories.

I decided to split the wheel in two parts, where all the flavors generally seen as positive are on the top half, and those generally seen as less desirable effects of roast or green coffee are placed on the bottom half. And while we’re talking about halves, why not make it look like a coffee bean ? I used an elliptical coordinate system to make it look a bit more like a coffee bean. Once you get familiar with these figures, they can tell you a lot about the coffee just from a quick glance, and I love that. Here are the ones I generated for the main varietals; there are similar figures for 30 varietals and 14 coffee processing methods (with high-resolution vectorial PDF versions) which I made available to my Patreon supporters (Bourbon-tier and up):

As you can see, Geisha is the king of floral attributes ! It’s also interesting how Bourbon and Caturra often have nutty flavors typically associated with roasting. It makes me wonder whether it’s harder to make great roasts out of them, but I don’t know enough about roasting.

Ranking Specific Flavors

There is yet another way of visualizing these data that would be interesting; that one is an idea from Scott Rao. I selected a few taste descriptors that are often sought for by coffee drinkers, and ranked the different varietals and processes by how often they come up in their respective categories. This time I didn’t normalize the fractions by how often they come up in all coffees, because it won’t affect the order of rankings. I did however add error bars (for the math geeks, Poisson errors) to represent the small-number statistics; in other words, when a given varietal/process is represented with less bags, the true fraction of how often it’s described with one word will be more uncertain because we don’t have enough data to constrain it well.

Something interesting Matt Perger noticed in the “Sweet” figure is that smaller beans varietals tend to be on the sweeter side, which could be explained by the more even surface versus core roasting of small beans.

I hope you found this analysis as interesting as I did ! I’d like to thank Scott Rao, Matt Perger and Patrick Liu for useful thoughts and comments, as well as the developers of the Firstbloom app again !

Now, here are more figures I generated ! I made many more ranking figures, available to my Patreon supporters.

Varietal Word Clouds

Processing Word Clouds

If you loved the figures in this post, there are many more like them available to my Bourbon-tier Patreon supporters here, for 30 coffee varietals and 14 processing methods !

Why do Percolation and Immersion Coffee Taste so Different ?

The picture above sent by my friend Francisco Quijano is an awesome demonstration of how different a V60 (left) and Aeropress (right) brews of the same coffee may look like.

I’d like to talk about why coffee brewed by immersion (e.g. french press, Aeropress, siphon) tastes so much different, and even look so different, than coffee prepared by percolation (e.g. pour over or drip). Some of you may have noticed that this holds even when you compare them at similar extraction yields and concentrations.

In a previous post, I talked about a more general equation for extraction yield that should provide a better correlation with the chemical profile of a coffee cup, and therefore with its taste profile. Obviously, it doesn’t capture effects like changing coffee, roast curve, or even grind size. But there’s something else fundamental that the general equation cannot capture, because the taste profiles generated by immersion and percolation brews just live in different landscapes. Today I want to explore why that is.

The crucial difference between a percolation and an immersion is simple: a percolation extracts coffee with clean water, and an immersion extracts coffee with water that is gradually becoming more and more concentrated, because water sits in with the coffee grounds for the whole brew.

Because of this, the speed of extraction levels off more quickly in an immersion brew. This arises from the physics of diffusion; any solvent more concentrated in a specific chemical compound will have a much harder time extracting that same compound from the coffee grounds. This concept is described by the Noyes-Whitney equation:

You can read more about the different terms of this equation here, but basically this just tells you that the rate at which a compound gets extracted is higher when the solution is much less concentrated in it than the coffee particle.

So far, it would seem like this only explains why an immersion would extract slower, not why it would extract a different profile of chemical compounds. But there’s a catch: even if water is concentrated in a specific compound, it doesn’t prevent it from extracting other compounds efficiently. Therefore, if you wait long enough, an immersion brew will very closely reflect the chemical composition that was initially in the coffee bean, as each individual chemical compound comes to balance with the slurry. If you stop the brew before everything is extracted (which we usually do), the slowest-extracting compounds will be a little bit underrepresented, but otherwise the chemical composition of your cup will be a pretty good reflection of the chemical composition in the coffee bean.

In a percolation brew, things happen very differently. This is true because at every moment, the slurry water is replaced with cleaner water, therefore forcing the extraction speed to remain high as long as it’s not depleted from the coffee bean. As you might deduce, this means that the fast-extracting compounds will be over-represented in a percolation brew.

In other words, the chemical profile of a percolation brew will be very strongly correlated with their extraction speed, whereas an immersion brew will be instead strongly correlated with how abundant each chemical compound is in the coffee bean. It’s like listening to music with two different equalizers on.

I like explanations with words, but I like figures even more. We can explore the difference between percolation and immersion brews by simulating two different brews with a very simple toy model, based on solving the Noyes-Whitney equation numerically. In the percolation case, the slurry concentration term will always be forced to zero as we constantly replace the slurry with fresh water.

Let’s imagine we have a coffee bean with 30 different chemical compounds; and put them in a coffee bean with different abundances and different extraction speeds. I generated 30 such chemical compounds at random, and obtained this distribution: 

Each red circle here is one of 30 simulated chemical compounds. Those further to the right are present in larger quantities, and those further up are easier to extract.

Now, let’s solve the Noyes-Whitney equation for one of them. Here’s how the brew concentration goes up over time for the fastest-extracting compound:

This should be nothing surprising: the extraction speed levels off much earlier during the immersion brew, because the slurry water becomes too concentrated. In the percolation brew, the extraction is still happening for as long as the chemical isn’t depleted from the coffee particles.

Now, we want to compare these two beverages at the same extraction yield. To do this, I generated the extraction of all 30 compounds simultaneously, and stopped the brew when the average extraction yield reached 20.0%. I made the assumption that the chemical compounds that can be extracted from the bean amount for 28.0% of its mass. Unsurprisingly, the immersion brew took a bit more time to reach that average extraction yield.

Something really fun we can do with this simulation is look at the profile of chemicals in the final cup for the immersion versus percolation, and compare it with the chemical abundances in the coffee bean. This is what we get:

Each bar in this figure represents one of the 30 chemical compounds we generated randomly. I placed them in order of extraction speed; those further to the right extract faster.

One thing that immediately jumps is how the immersion brew (red) is much more similar to the internal coffee composition (black) compared to the percolation brew (blue). The only difference lies in the compounds that are slowest at extracting, as expected. If we let the immersion brew continue, this difference would become smaller and smaller, and eventually subside completely.

The percolation brew looks quite dramatically different from the internal composition of the coffee bean ! As you can see, those compounds that extract fast become completely over-represented compared to the internal coffee composition.

As it’s already quite clear from the figure above, an immersion brew composition correlates mostly with the abundance of chemicals inside the coffee bean:

This correlation is quite strong as you can see, with the exception of the 6 slowest compounds that are still out of balance because we stopped the brew before an average extraction yield of 28.0%.

Here’s another interesting observation: a percolation brew correlates strongly with how fast each chemical compound can extract:

As you can see above, the compounds further to the right are much more represented in the cup of percolation coffee, whereas they are not necessarily over-represented in the cup of immersion coffee.

All of these considerations only hold true because we stop the brew before the maximum theoretical extraction ceiling. If we were to extract everything from the coffee beans, then obviously the immersion and percolation brews would end up with the exact same chemical profiles, the brew times would just be different, and the concentrations would also be different if you used different quantities of brew water. To demonstrate this, I let the simulation run all the way to 28.0% and made a video of how the flavor profiles extract. You can see that, although the beverages converge to different concentrations, they both end up with the same profile than the coffee bean composition:

Obviously, there are other complicating factors that can make different types of brew even more different. For example, the presence of channeling in a percolation brew can bring out a lot more of the slow-extracting (usually astringent) compounds from a small fraction of the coffee particles, which as far as I know never happens in an immersion brew. But if you make sure to minimize channels in your coffee (I give some tricks on how to do that in my V60 recipe and pour over video), this won’t be a significant effect.

Another potential difference is suspended solids. Those are almost always filtered out by the bed of coffee itself in a percolation brew, whereas they will remain in your cup in simpler immersion brew methods like the french press. These compounds can have a strong effect on taste (usually muting it), even if they are not dissolved in water.

I’m sure some of you were surprised when I listed the siphon and Aeropress as examples of immersion brews at the start of this post. I know they are mixed methods, but in practice their tastes bear more resemblance to an immersion. I suspect that the reason for that is simply that most of the extraction happens during the initial immersion phase, not during the subsequent percolation phase. But surely, their chemical profile probably looks like some average of the percolation and immersion profiles.

You might think that this whole post is defeating the usefulness of the general extraction yield equation I mentioned before, but I don’t think it is. I will need a mass spectrometer to prove it, but I think that (1) for a fixed coffee and method, it will make the extraction yield measurement depend less on the amount of retained water; and (2) for different brew methods, it will make the comparison a little bit better, even if it’s never perfect. The comparison will certainly be made much better for two different methods in the same category, e.g. a Buchner percolation (without immersion phase) and a V60.

Before closing, I’d like to add a caveat to the analysis above; what I carried here is a simulation of random chemical compounds that don’t necessarily exist, just to demonstrate the concept of how extraction happens differently in immersion versus percolation. It is a dimension-less analysis (i.e. it does not involve any physical units), and therefore it does not indicate how significant these differences between percolation and immersion are. I do not know whether they are the cause for 1% or 50% of the taste difference between percolation and immersion (the rest of the difference would be colloids, fines, etc.), but my guess is that it is much less than 50%. One way to test this would be to perform blind test comparisons of a Hario immersion switch and V60 brews, but keeping all other variables constant will be a real challenge – just think of how the slurry temperature evolves during the brew in both cases; depending on the kettle temperature, constantly changing the brew water versus keeping the same water in an immersion will have a significant effect on the temperature profile, unless extreme caution and precise instruments are used !

I’d like to thank Francisco Quijano for sending me his awesome photo that serves as this blog post’s header, and Matt Perger for useful comments. I’d like to thank Aurelien He for proofreading comments.

The Repeatability of Manual V60 Pour Overs

Today I decided to measure how repeatable and consistent my manual V60 pour overs are. My expectations were very low, given how variable an average extraction yield I often get when I brew the same coffee a few days apart.

To do this, I used some older coffee I had left from a local roaster to prepare five V60 pour overs in a row. I started by preparing a gallon of water with the Rao/Perger water recipe described here so that I wouldn’t need to switch gallon, and to therefore mitigate any possible manipulation error when I prepare my brew water. The coffee beans I used are the Quintero Ignacio Colombian (a mix of Caturra, Typica and Tabi varietals) from Saint-Henri coffee roasters, roasted on February 25 2019, which I kept vacuum sealed in the freezer between then and the date of the experiment, May 26 2019. I took the beans out of the freezer about a week before the experiment, and opened the vac sealed bag right before brewing. Its roast profile is on the slightly dark side, where you get some hints of smoky flavors.

I used grind setting 7.0 at a 700 RPM motor speed on my Weber Workshops EG-1 grinder. It is zeroed so that burrs touch completely at 0.0, so 7.0 means that the burrs are spaced 350 microns apart. I used the plastic Hario V60 with the tabless Hario V60 bleached filters. I used the brew recipe that I described in this post and that follows Scott Rao’s method except for a few modifications. You can also find a video of this method here (pardon my poor filming skills, I will eventually make a better video).

I used a 22 grams dose and a total water weight as close as possible to 374 grams to achieve a 1:17 ratio. I prepared a nest shape with chopsticks as I described here. I tried to aim for 77 grams of bloom water; this is a bit higher than the 3:1 bloom ratio recommended Scott Rao, but I typically find it easier to quickly wet all grounds with that much water. I “rao-spun” the bloom quite heavily after pouring ~77 grams of water in, to ensure that all grounds are wet, and I used a chopstick to pop any bubbles that were forming. I did not use a spoon to stir the bloom. I used a 45 seconds bloom in all cases.

I pre-heated the kettle to 187°F while I was grinding the dose, pre-wetting the filter thoroughly (first with tap water and then with brew water), and preparing the coffee bed. I then boiled the water to 212°F right when I needed it, to avoid having minerals precipitate during a long boil (I’m not sure yet how important this effect is). I did not click my grinder, which causes it to retain 0.5 grams coffee instead of < 0.1 grams, but this also causes much less chaff and fines to be present in the dose because they preferentially stick to the grinder chute. I also used the Weber dose preparation shaker, which helps distribute fines uniformly throughout the coffee bed.

I tried to be as consistent as possible during my five brews – I think the hardest part is keeping a constant flow rate (the newer Acaia Model S scale may help with that because it apparently measures live flow rate, but I don’t have it), which resulted in slightly different brew times. I always initiated the second pour at 1:45, which helps discriminating which part I poured faster or slower when the times differ. I used the Brewista artisan gooseneck kettle which helps achieving a consistent flow rate, but it also means I had to press “quick boil” again every time I put the kettle back on its base (turns out I did not forget to do it during the five brews).

All brews had a very flat coffee bed at the end, and all were level except for the fourth brew which was very slightly slanted with the higher up side away from me (i.e. water drew down at the furthest point from me less than half a second before the closest point). When the surface of water passed that of the coffee bed and I could see light reflecting on the surface of the wet coffee bed, I noted the brew time, waited about 3 seconds and placed the V60 on top of a small recipient with the same aperture than the plastic V60 inner plastic ring. I gently swung the V60 up and down to collect 5-10 drops of coffee to determine the approximate concentration of interstitial liquid in the slurry at the end of the brew. This is useful to determine a more accurate average extraction yield that is more independent of the amount of retained water; for a detailed discussion on this, you can see this blog post and this one too.

I cleaned the VST refractometer lens with alcohol and re-zeroed it with distilled water, then measured the concentration of the last few drops and of the beverage using the recommendations of Scott Rao (also see this awesome guide by Mitch Hale). During this experiment, I realized that even if your refractometer measures a 0.00% concentration for distilled water, it is still very important to re-zero it; my TDS readings would otherwise be 0.10% too low because the weather is getting warmer in Montreal and I had not re-zeroed in more than a month ! You can find more details about this on my Instagram page.

Here’s how the five brews ended up comparing to each other:

Weight of bloom water:

  • Brew 1: 77 grams
  • Brew 2: 75 grams
  • Brew 3: 76 grams
  • Brew 4: 77 grams
  • Brew 5: 77 grams

Full span: 2 grams
Standard deviation: 0.9 ± 0.2 grams

Time where I reached 200 grams:

  • Brew 1: 1:07
  • Brew 2: 1:11
  • Brew 3: 1:11
  • Brew 4: 1:10
  • Brew 5: 1:09

Full span: 4 seconds
Standard deviation: 1.6 ± 0.3 seconds

Time where I reached total water weight:

  • Brew 1: 2:25
  • Brew 2: 2:23
  • Brew 3: 2:23
  • Brew 4: 2:19
  • Brew 5: 2:13

Full span: 12 seconds
Standard deviation: 5 ± 1 seconds

Total time at drawdown:

  • Brew 1: 3:04
  • Brew 2: 3:09
  • Brew 3: 3:05
  • Brew 4: 3:10
  • Brew 5: 3:08

Full span: 6 seconds
Standard deviation: 2.6 ± 0.4 seconds

Beverage weight:

  • Brew 1: 322.3 grams
  • Brew 2: 325.6 grams
  • Brew 3: 325.5 grams
  • Brew 4: 325.9 grams
  • Brew 5: 325.5 grams

Full span: 3.6 grams
Standard deviation: 1.5 ± 0.4 grams

Concentration of the last few drops:

  • Brew 1: 0.59%
  • Brew 2: 0.58%
  • Brew 3: 0.56%
  • Brew 4: 0.51%
  • Brew 5: 0.47%

Full span: 0.12%
Standard deviation: 0.051 ± 0.009%

Concentration of the beverage:

  • Brew 1: 1.42%
  • Brew 2: 1.41%
  • Brew 3: 1.42%
  • Brew 4: 1.43%
  • Brew 5: 1.43%

Full span: 0.02%
Standard deviation: 0.008 ± 0.002 %

Liquid retained ratio:

  • Brew 1: 2.6
  • Brew 2: 2.5
  • Brew 3: 2.5
  • Brew 4: 2.4
  • Brew 5: 2.5

Full span: 0.2
Standard deviation: 0.07 ± 0.02

Approximate “shareable” average extraction yield:

  • Brew 1: 20.8%
  • Brew 2: 20.9%
  • Brew 3: 21.0%
  • Brew 4: 21.2%
  • Brew 5: 21.2%

Full span: 0.4%
Standard deviation: 0.18 ± 0.03%

Precise average extraction yield (assuming f_abs = 1):

  • Brew 1: 21.6%
  • Brew 2: 21.6%
  • Brew 3: 21.7%
  • Brew 4: 21.8%
  • Brew 5: 21.7%

Full span: 0.2%
Standard deviation: 0.08 ± 0.02%

As you can see, my timings varied by some amount, but the effect on the concentration of total dissolved solids and average extraction yields were quite small. Another really interesting part is the fact that the approximate “shareable” average extraction yields varied by more than those calculated with the more exact formula. This may be explained by the fact that the more exact formula better compensates for different liquid retained ratios, likely caused by my having waited less or more before I removed the V60 from the coffee pot.

I honestly did not expect to reach a consistency of < 0.02%, close to the inherent precision of the VST refractometer (0.01%), but it seems that with enough concentration it is possible ! I do not think that I can reach this kind of accuracy first thing in the morning when I usually prepare my coffee. This experiment did teach me something important however: it is of utmost importance to be really careful in cleaning up the VST lens with alcohol, properly re-zero it with distilled water, and be patient while the sample reaches the lens and room temperature. Neglecting any of these steps can cause measurement errors much larger than 0.02% !

A V60 Pour Over Video

Today I decided to release publicly one of the V60 videos from my Patreon. I plan to make a better quality video eventually for my blog, but in the meantime I thought this would be interesting to a wider audience. Please view this recent post I made about what is going on with Patreon if you are worried that I’m making some of my content access-restricted, and this previous blog post explains the method I use here in more details.

A video of me brewing a V60 pour over

You can find a higher-resolution version of this video here, but be warned that it is 1.2 GB large !

In this video I’m brewing Gardelli’s Ethiopian natural Chiriku with a 1:17 ratio and 22 grams dose. I used grind setting 6.8, slightly finer than my usual 7.0@700RPM, because last time I brewed this coffee, it felt a bit watery. Turns out I preferred it at 6.8, and I rarely get astringency at that grind setting. I’ll tell you more about that in a different post, but I now suspect that the average mass of coffee particles is an important factor that determines channeling, because it has a lot to do with the structural integrity of the coffee bed. I therefore suspect that there is a lower limit in grind size that will get you some astringency very easily for a fixed brew technique; it corresponds to the point where channels are being dug by water. Most of the time I still use a 7.0 grind setting, just to be sure.

You will notice in this video that I spin a bit harder than I used to. This is partly because I was being too gentle especially in the first video, but it is also because I realized I have so little fines with the EG-1 grinder + SSP ultra low-fines burrs that fines migration is not as much of an issue compared to other grinders. I suggest to start very gentle, and then try more brews (with the same coffee) where you gradually spin a bit harder. If your brew time goes up significantly, then you might want to go a little easier to avoid fines migrating to the bottom of the brewer. You’ll have to find your own pace, as I suspect it depends (slightly) on the grinder you’re using; in general, a higher quality grinder should allow you to spin a bit harder.

I had pre-rinsed my Hario tabless filter before starting the video, first with a lot of tap water and then with a bit of warm brew water. The kettle was also preheated at 189F before I started the video. My pours will all be made with boiling water, but preheating it at 189F means I’ll have to wait less when I’m ready to pour. The first thing I do is weight and grind my beans – I weighed 22.3 grams and ground 1-2 beans to make sure nothing was stuck on the grinder burrs from yesterday’s brew. I then cleaned up my blind shaker and placed it back on for the main grind.

You’ll notice that during the bloom pour, I don’t concentrate too much on my pour technique: I move horizontally a bit too fast and I also move vertically which I ideally shouldn’t. Instead, I make sure I have high flow and to stop at the right amount. My goal here is to wet everything quickly rather than immediately getting a perfectly level bed. I’m also giving it a much more thorough spin after that pour because I found that helps with getting everything wet at once.

You can see that I spent a short amount of time removing the high & dry grounds with my pours, but otherwise I described a very slow flower pattern that hits the center more often than the sides. I’m trying to get the whole bed agitated by doing that, with more focus on the center because there’s more layers of coffee there. I move very slowly because I want the water to fall very straight (this helps getting a flat coffee bed), and I don’t move vertically. I try to get a very steady flow too, but that’s the part I’m still the worst at without the ability to measure it on-the-go.

When I spin after the first pour to 200 grams, you can see that two bubbles appeared. That is generally not a good sign, as it means some brew water just touched dry coffee. The fact that it happens while I was spinning tells me that I probably just destroyed a channel and forced the water to flow through dry coffee. That doesn’t mean the brew will necessarily be bad, but it means I could have done a better job during the bloom phase. It happens to me 5 times in the last 14 brews, so about a third of the time. This is one reason why I’d really like to have a plastic V60 brewer with a steep & release mechanism (I know about the Clever but I don’t like its shape); it would allow me to stop water from flowing during the bloom, and probably give me enough time & control that I would be comfortable with mixing the bloom with a small spoon.

If you wonder why I tap the cork lid before putting it on the V60, it’s not from an obsessive compulsive disorder, but rather to make sure that there’s no coffee grounds on it (or at least I like to tell myself that).

Notice how clear the water is at the end of the drawdown. This is because the EG-1 with SSP burrs produces a crazy small amount of fines at the optimal V60 grind size. It reminds me of when I experimented with the Melodrip, but now I get even after having agitated the coffee bed. If you pay attention at the end you’ll see that I stop the scale’s timer exactly when the reflection of light from water above the coffee bed ceases because water just went below the height of the coffee bed. I like to use this cue because it’s very repeatable, and it might help you compare your own brew times with mine more precisely.

At the end of the brew, I let the V60 drip a bit more into the beverage, then I place the V60 on top of a small glass and gently move it up and down to get a few more drips and measure the approximate TDS of the slurry at the end of the brew.

After that, I clean up the refractometer and measure the beverage TDS, but I make sure to taste it before looking at the TDS measurement, otherwise I found that it can affect my taste perception. Also notice how I mix the brew with a spoon before sampling it; this is better at mixing up all coffee layers than just spinning the brew.

I know the ending is a bit abrupt, sorry about that – my iPhone ran out of storage ! You just missed the brew TDS measurement. I’m starting to be more satisfied with this angle of view, so I’ll start thinking about how I can make a more complete brew video that I can eventually publish on my blog. I’ll make sure I don’t wear slippers for that one.

Here are the relevant measurements for this brew:

  • Coffee: Gardelli Chiriku Ethiopian Natural
  • Grind size: 6.8 at 700 RPM
  • Ratio: 1:17
  • Dose: 22 grams
  • Water: 374 grams
  • Bloom water weight: 77 grams
  • Time at the end of first pour (200 grams): 1:08
  • Time where second pour is initiated: 1:45
  • Time at the end of second pour (374 grams): 2:20
  • Total brew time: 4:03
  • Beverage weight: 319.9 grams
  • TDS of last drops: 0.94 %
  • TDS of beverage: 1.43%
  • Approximate EY (percolation equation): 20.8 %
  • More accurate EY (general equation): 22.4%

I hope you enjoyed it, and don’t hesitate to leave a comment if you have questions.

I’d like to thank Scott Rao for his tremendous help in improving my pour over technique. The method above is also strongly inspired from his method !

About Patreon

I realize I haven’t talked a lot about my Patreon page on this blog yet, so I thought I’d update you all about it in a short blog post. I might remove it later, if it becomes irrelevant, and because I am trying to make this blog a repository of useful resources rather than updates on my whereabouts (for that, you can see my Instagram).

The reason I created a Patreon is to buy some expensive equipment that will allow me to push my coffee posts further, but rest assured I have no intention for these posts to remain only accessible on Patreon. You can find more about these future plans in one of the public posts I wrote on Patreon “Some Future Projects I Have in Mind“. There are a few more posts directly on my Patreon that are public and won’t make it to this blog, because I they are not directly relevant to it, or I don’t feel their content is best explained there.

I don’t want anyone to feel forced to contribute to my Patreon, rather I’d like it to be only for the more “hardcore” fans who really want to contribute regardless. I do offer some benefits to my backers following the Patreon model with tiered donations, but these benefits are either not refined enough for being on my blog yet, or they are things that I never planned to share publicly on this blog. For example, I share multiple Patreon-only videos that are “in development”, either because the quality is not there yet, or because the content is not final. Stay tuned for such a video to be released here later today.

An example of something I do not plan to share publicly is my (almost) live-updated personal coffee log (although I will share some stats about it), and my running list of experience with different roasters. I do eventually share publicly the roasters that I prefer, but I don’t share publicly those that I didn’t like – I feel like this would be a bit too hostile. So in conclusion, I view my Patreon as a “backstage” access to the stuff that is in development, rather than anything that should replace the blog posts that I will keep making public here.

I’m hoping this will address some fears I read about online, and stay tuned for a V60 brew video later today !

Seasoning Grinder Burrs and Grind Quality

[Edit May 28, 2019: The violin plot and two of the other plots below had an axis that stated micron squared and should have been millimeters squared; those are now fixed. Thanks to Mark Burness for noticing !].

As some of you know, I recently decided to make the move and get the Lyn Weber EG-1 grinder with the SSP Ultra low fines burrs. I took this decision mainly because I heard this combination generates the lowest amount of fines other than industrial roller mill grinders, but also because of its design focused on single dosing and low grind retention. I like to switch coffee every brew, so those are very nice features for me. I’ll make a more detailed post where I compare the EG-1 with my previous Baratza Forté, but in the mean time I’d like to talk about burr seasoning.

The EG-1 grinder by Lyn Weber. This is what all grinders should look like.

The Seasoning

If you never heard the term seasoning, it refers to the habit of grinding a large quantity of roasted coffee (or even rice) to break in grinder burrs which initially have harsh angles and corners. It is often said that this is done to prevent grind size from changing with use, and to obtain a more uniform grind distribution, which maximizes the average extraction yield of good-tasting espresso or pour over brews. When I seasoned my Baratza Forté, I did it with 12 pounds of roasted coffee at espresso grind size. Back then, I didn’t have a good way to measure the particle size distribution of my grinder, and I just supposed that I was done.

It is possible to diagnose whether you are done seasoning your grinder with a refractometer, by actually brewing coffee and noting the maximum average extraction yield you are able to reach without getting astringent taste. This typically takes me a couple of brews, and giving the limited time I had to do this I just ground a large amount of coffee and called it a day.

Now that I wrote an application to actually measure grind size distributions, I decided to take a sample of coffee every few pounds while I was seasoning the SSP burrs of my EG-1 grinder. I zeroed the grinder position at grind setting 0.0, which means that this is the point where burrs touched (I can hear burrs that start to rub against each other at grind setting 1.5). I initially started seasoning 2 pounds with a 700 RPM (revolutions per minute) motor speed and grind setting 8.5, which means that the burrs were 425 microns apart; turns out this was closer to a V60 grind size, so I went down to grind setting 5.0 (250 micron burr spacing) and 800 RPM after that. The slightly higher motor speed made sure that the motor didn’t stop from time to time as I fed a lot of coffee in the grinder. After 12 pounds, I even went a bit faster (1000 RPM) for the same reason. I sticked with this setting all the way to 24 pounds; I went all the way to 24 pounds because I heard the SSP burrs were particularly hard to break in.

I used a collection of beans from bad roast batches at my local roaster to do the seasoning, so they consisted in mix of roast profiles and bean varietals. However, after every 2 pounds of seasoning with the mixed coffee, I always took a small ~10 grams sample of the same bean, a washed Bourbon from Burundi (roasted by my friend Andy Kires at the Canadian Roasting Society), which came from a single roast batch. I always made sure to purge the grinder of any grounds from the seasoning before collecting the sample, and I ground and threw away a small amount  of the Burundi just before grinding the actual sample to make sure none of the seasoning coffee was left in. I always collected the Burundi samples at grind setting 8.5 (425 micron burr spacing) with a 700 RPM motor speed.

The Particle Size Distributions

I decided to measure the particle size distribution of half the samples (every 4 pounds), because this takes a crazy amount of work; for each sample, I took 12 images that I analyzed and combined with my grind size application. I didn’t count exactly how many hours this took, but it was about 2 seasons of The Office.

In this figure, the thickness of the horizontal band represents the total mass of the particles at each particle surface (this is called a violin plot and it’s great to compare several distributions together). This allowed me to see for the first time how the particle distribution moves to coarser particles as the burrs are breaking in. It makes a lot of sense that the distribution moves to coarser sizes, as the more rounded edges of the burr’s teeth should allow slightly coarser particles to pass through.

In the figure above, I show how the average particle surface changed with the total seasoning weight. The error bars are based on small number statistics (for the statistics geeks, they are based on Poisson distributions), and represent the fundamental limit in precisely measuring the average particle surface from the limited number of particles that I analyzed (typically approximately 15,000 particles, which is what 12 photos on a standard white sheet of paper gets you).

Notice how the 16 pounds data point seems off from the general trend. I strongly suspect this was caused by me forgetting to set the motor speed to 700 RPM when taking the Burundi sample – leaving the motor speed at the 1000 RPM I used for seasoning would make the particle spread distribution finer on average. This is an effect I also observed with my app, but this will be for another blog post.

One thing that I found particularly interesting is the fact that, even when the particle distribution stabilizes and stops moving to coarser particle sizes, it kept becoming more uniform. I can’t say for sure that this happens on all burrs and all grinders, but this is a good thing ! I found it amusing that I stopped seasoning within 4 pounds of where the shifting of the particle size distribution stopped being detectable with high statistical confidence with my 12 photos. One thing that hit me when I saw this figure is that it resembles a relation that exponentially approaches an asymptote, like a lot of other things in life; another example of such a relation is the concentration of water versus time in an immersion brew.

Grinder Quality Factors

Another interesting relation to look at is how the width of the particle size distribution evolves with seasoning weight. I did this by looking at its standard deviation:

In the figure above, the error bars are similarly based on small number statistics. What we see here is a little different; the distribution initially becomes wider, but then it starts becoming narrower (more uniform). In my experience, particle size distributions that are centered on coarser particle sizes always seem to be wider. This is what led me to define something called the Q-factor (for “quality” factor) in my grind size app, which is simply the ratio of the average particle surface divided by the standard deviation of the particle surface distribution. This ratio seems to be relatively constant across grind sizes (at least in the neighborhood of filter brews), and it also seems to go up with grinder quality. I’ll get back to this in more detail in a future blog post, but here are typical Q-factors that I started compiling for different grinders:

  • A friend’s Mahlkonig EK43* after aligning with shims: 1.45 ± 0.02
  • Baratza Forté BG*: 1.53 ± 0.01
  • My EG-1 with SSP burrs before seasoning: 1.59 ± 0.02
  • An older EK43* model that another friend carefully aligned: 1.61 ± 0.01
  • My EG-1 with SSP burrs after seasoning: 1.76 ± 0.02

An asterix indicates a grinder with its original stock burrs.[Update May 17 2019: Stay tuned for a more complete list of Q-factors that will evolve over time and be accessible to Honey Geisha-tier patrons.]

Gathering these data takes a tremendous amount of work, but I’m gradually building up a library of quality factors for different grinders that I managed to get my hands on. My Patreon followers can already access that partial list as I build it up, but I will eventually release it to the public; it will take a while for me to finish this up however.

This led me to think that a more interesting way to look at how my particle distributions evolve through seasoning is to look at their Q-factor versus seasoning weight:

As you can see, the Q-factor didn’t change much at first while the particle distribution shifted to coarser grind sizes (it hovered around ~1.55, similar to a re-aligned EK43), but then it started increasing by quite a lot.

Eventually, I will map out precise particle size distributions for several different grind sizes with my fully seasoned EG-1. This will allow me to compare each of the particle size distribution above with a fully seasoned distribution at the same average grind size, and thus to say more precisely how the distribution narrowed versus seasoning weight, without having to make the assumption that the Q-factor is perfectly independent of grind size. But this will also take many more seasons of The Office 🙂

More seasoning and an Interesting Observation

When I left my friend’s roaster place after having seasoned the EG-1 with 24 pounds of coffee, I grabbed a bit more of his Burundi and put it in a sealed opaque bag with a 1-way valve and an oxygen absorbing pad (see my other blog post about keeping your coffee fresh for why this is good practice). I did this with the plan to eventually season the grinder a bit more with a 4 pounds bag of bad coffee I had at home. It took me 23 days (and 3.5 pounds of filter pour over coffee that I actually drank) before I had the time to do so. Fortunately, I had the good idea to take a sample before this additional seasoning, as well as after. The effect of this additional seasoning on the particle size distribution was very small, as expected:

There is one thing that really surprised me however; if I compared the grind size distribution right before seasoning again to that right after my first seasoning, it actually became much finer and slightly wider, as you can see in this next figure !

It is highly unlikely that this was caused by the additional 3.5 pounds of coffee that I ground at filter size, because (1) grinding this coarse has a much smaller effect on breaking in the burrs; and (2) this goes exactly the other way than what seasoning does (as we saw above, it makes the particle distribution coarser and narrower, not finer and wider !).

My best hypothesis for what happens here is this: I think that the coffee beans de-gassed and dried as they aged, and the cellulose structure of the beans may also have weakened form the aging. All of these effects will make it easier for the beans to shatter, which will produce more fines, therefore shifting the particle distribution to finer average sizes and widening it. This is exactly what happens with decaffeinated coffee, which requires grinding at slightly larger grind sizes than regular coffee. This will be the subject of a different post, but some extensive blind-tasting dialing in had me select an optimal grind size of 7.5 (375 micron burr spacing) for Heart‘s Colombian decaffeinated coffee, whereas I selected 7.0 (350 micron  burr spacing) for several different caffeinated beans; you can also see this nice coffee tip of the day from Scott Rao about brewing decaffeinated coffee.

I found this possible explanation so interesting that I plan to do more experimentation about it, to determine exactly how particle size distributions shift with aging. Imaging knowing exactly how coarser your optimal grind will change versus the age of your coffee, without needing to dial in again. I would definitely love that !

Disclaimer: Doug Weber generously offered me the SSP Ultra low fines burrs when I bought the EG-1 (under no obligations). I decided to get this grinder based on my friend Mitch’s recommendation and my own research on available grinders, and I receive no benefits from Lyn Weber.

Grind Quality and the Popcorning Effect

I often heard worries in the coffee community about a difference of quality in the coffee grind size distribution when grinding with a full hopper versus a single dose of coffee in an otherwise empty hopper.

The idea behind this is that coffee beans forced through the rotating grinder burrs have no choice but to go through whatever openings they encounter between the burrs. In contrast to this, a single bean in an empty hopper will bounce around and may end up passing through a larger hole between the burrs when the opportunity arises, because nothing is forcing it to pass through very fast. This bouncing around of a bean is what “popcorning” refers to.

As a result of this effect, beans that popcorn will end up getting ground somewhat coarser on average. Grinding a single dose of coffee in an otherwise empty hopper will therefore generate two kinds of coffee grounds: a first batch of slightly finer grounds resulting from beans forced through the burrs, plus a smaller batch of slightly coarser grounds resulting from the last beans that popcorned. The result will be a distribution of coffee particles slightly wider than what you would have obtained if you ground a small dose of coffee with a full hopper.

This more uneven distribution of grinds will cause an increase in the amount of coffee particles larger than average, sometimes called boulders. As I mentioned before on this blog (e.g. see this article), only the surfaces of coffee particles extract efficiently when you brew the coffee, and this larger amount of boulders will limit the amount of coffee compounds that you are able to extract quickly and evenly. Several people therefore suggested that it is best practice to grind with a full hopper, and even to grind one bean at a time if you are extremely patient and want to grind a single dose of coffee at a time.

Now that I built a tool to measure particle size distributions, I decided to test all of these claims. They all make sense, but none of these arguments are really telling us how important this effect is. To do this, I ground 3 different doses of 10 grams each on my Baratza Forté BG grinder. I used the same coffee for all these tests, which is important (especially the roast profile may affect how the coffee shatters). In this particular case, I used a relatively light roast of an Ethiopian Guji by Saint-Henri roasters in Montreal. I ground them on setting 6L with the factory-set zero position. In my case, this means burrs would only touch if I went 3-4 ticks finer than 1A. The first dose was ground with a hopper full of beans, the second one was ground by dropping just 10 grams of coffee beans in an empty hopper, and the third one was ground one bean at a time. This last batch bored me to hell.

I measured the particle distribution of each dose by taking 12 different samples sprayed on a 8.5″ by 11″ sheet of paper and combining them together. I took that many samples to make sure that I would have good statistics to be able to resolve minute differences in particle size distributions. I decided on the number 12 because I noticed that comparing the first 6 data sets combined together looked similar to the last 6 combined together when binning the particle size distributions in 16 distinct particle surfaces, so having double that amount of data seemed conservatively good enough.

As a first test, we can ask ourselves how important the popcorning effect is, i.e. how much coarser do the grounds come out compared to beans forced into the burrs ? To do this, we need to compare the full hopper versus the bean-by-bean doses.

What I call the “fraction of available mass” in this figure is the mass of coffee that is available for extraction if you assume that only outer shells of 100 micron are extracted in each coffee particle. This is just an approximation, but it is already more meaningful than just looking at the total mass of coffee particles. For more information, I suggest reading this previous blog post where I discuss a very interesting experiment carried by Barista Hustle to explain why this approximation makes sense. Basically, we want our particle size distributions to contain some information about how the coffee will extract, so we don’t care about weighing the cores of coffee particles that will never be extracted. I also talked about this more here and here. Another thing to notice in the figure above is that the horizontal axis indicating particle surfaces is in logarithmic scale. This means that every shift of e.g. 60 pixels to the right corresponds to a particle size twice as large. On top of each distribution, there is also a single data point with horizontal error bars, that respectively indicate the average particle surface and the spread of the distribution on each side.

As you can see, we are able to see a difference, albeit a small one: the beans ground one at a time are indeed about 0.08 mm² coarser than those ground with a full hopper. To get a better sense of how coarser they are, I compared the bean-by-bean dose to other full-hopper grind sizes on my Forté, and determined that the closest match was to setting 6Q:

Another interesting part of this is that grinding bean by bean generates a slightly tighter distribution, therefore mimicking a higher quality grinder. It might seem tempting to adopt this practice, but do it once and you’ll see why no one does it. It is also possible that this is just an effect of having started the grinder motor before the first bean hits it; this means the motor was rotating at the same exact speed during the full grind. The “full hopper” and “empty hopper” data sets were taken with coffee already dropped on the burrs before the grinder was started, therefore the start of the dose was grinder at a slower motor speed while it was speeding up. I am under the impression that this doesn’t entirely explain “bean by bean” doing so much better, but I will be isolating out this effect very soon to test that hypothesis 🙂

As we saw, popcorning beans are ground approximately 5 clicks coarser on the Baratza Forté BG. A strategy suggested by Scott Rao to grind a single dose was to start at your desired grind setting, and then change your grind size to something slightly finer when you see that your beans start popcorning. This figure above tells us that, if you wanted to do this, it would be appropriate to grind exactly 5 clicks finer when the beans start popcorning. That may require mastery of the on-the-spot Forté fine controls.

However, let’s first ask ourselves another interesting question; does popcorning affects enough beans to have any effect at all on the particle size distribution of a full 10 grams dose ? The smaller the dose, the bigger the effect will be, as the number of last beans bouncing around will always be the same. To answer this, let’s compare the particle size distributions of the full hopper versus empty hopper doses:

As you can see on this figure, the two distributions are virtually undistinguishable. This means that the popcorning affects such a small fraction of the 10 grams dose that I was not able to see any difference with this analysis. As you can imagine, the effect will be even smaller on typical doses which tend to be around 15 to 25 grams. As we saw previously, the last few popcorning beans were clearly affected and they were ground coarser, so there has to be a difference between the two particle size distributions even though it is a very small one. But to put this in perspective, the overall difference on a 10 grams dose has to be much smaller than one click on the Forté, and also much smaller than the difference in grind quality between all different brands of grinders I have ever tested. This includes Comandante’s C40, Orphan Espresso’s Lido 3, Mahlkonig’s EK43, Lyn Weber’s EG-1 and Baratza’s Forté BG. All of these grinders generate particle distributions that a similar analysis can easily distinguish.

This distribution illustrates how well the grind size app can distinguish between the quality of the grind distribution of the Lido 3 hand grinder versus the Baratza Forté BG grinder. The difference between an empty and full hopper seen in the last figure is minuscule compared to these cross-grinder differences.

The take out message that I got from this experiment is that popcorning has a non-negligible effect on grind size, but it affects a negligible amount of beans in any reasonable dose of coffee. You should therefore not be afraid to grind single doses at a time, because any degradation that results in your particle size distribution will be much smaller than any difference between brands of grinders. I’m hoping this post will alleviate the admittedly first-world and very geeky problem of single-dosing anxiety.

For those geek enough to ask or even to make it this far in the post, I did make my data public on Github.

I’d like to thank Douglas Weber for useful comments, and Victor Malherbe for proofreading.

An App to Measure your Coffee Grind Size Distribution

[Edit April 20 2021: Chris Satterlee generously developed install packages for both OS X and Windows here ! I’m very thankful for this help (it’s not straightforward at all to do this).]

[Edit April 25 2019: Please note this is not an iPhone or Android app, and I have no plans to release it as such. You can use your phone or any other camera to take pictures of your ground coffee, but then you need to install the application on either OS X or through Python (on any operating system) to analyze the data. Download the application package here.]

Today I would like to present an OS X application I have been developing for a few months. It turns out writing Python software for coffee is a great way to relax after a day of writing Python software for astrophysics.

When I started being interested in brewing specialty coffee a few years ago, one of the first things that irritated me was our inability to recommend grind sizes for different coffee brewing methods, or to compare the quality of different grinders in an objective way. Sure, some laboratories have laser diffraction equipment that can measure the size of all particles coming out of a grinder, but rare are the coffee geeks that have access to these multi-hundred thousands of dollars kinds of equipment.

At first, I decided to take pictures of my coffee grounds spread on a white sheet, and to use an old piece of software called ImageJ, developed by the National Institutes of Health mainly to analyze microscope images, to obtain a distribution of the sizes of my coffee grounds. This worked decently well, and allowed me to start comparing different grinders. Then Scott Rao made me realize that a stand-alone application that doesn’t need a complicated installation and that is dedicated to coffee would be of interest to many people in the coffee industry. Probably just the 10% geekiest of them, but that’s cool.

I’m hoping that this application will help us understand the effects of particle size distributions on the taste of coffee. I don’t think the industry really kept us in the loop with all the laser diffraction experiments, so hopefully we can help ourselves as a community.

If you are interested in measuring the particle size distribution of your grinder, then this app is for you ‒ and it’s free. I placed it as “open source” on GitHub, so if you are a developer, you are welcome to send me suggestions in the form of push requests (the developers will know what that means).

If you would like to get started, I suggest you read this quick installation guide, which will explain how to download the app and run it even though I am not a registered Apple Developer. Then, you can choose to either read this quick summary that will get you running with the basics, or this very detailed and wordy user manual that will guide you through all the detailed options the application offers you.

I would like to show you an example of what can be done with the software. Below, I am comparing the particle size distribution of the Baratza Forté grinder, which uses 54 mm flat steel burrs, with that of the Lido 3 hand grinder, which uses 48 mm conical steel burrs. I set both grinders in a way that produces a similar peak of average-sized particles with diameters around 1 mm, but as you can see, the particle size distributions are very different ! The Forté generates way less fines (with diameters below 0.5 mm) and slightly less boulders (with diameters of approximately 2 mm), which is indicative of a better quality grinder.

An example of figure that can be generated with the coffee grind size software. Each red bar corresponds to one kind of particle diameter generated by the Lido 3 grinder (smallest particles correspond to the leftmost bar, largest ones correspond to the rightmost bar), and their heights correspond to the total contribution of these kinds of particles, by mass. As you can see, the particles that contribute to the largest amount of mass have sizes just above 1 mm. The red circle shows the average particle diameter for the Lido 3, and the horizontal bars show the “characteristic width” of the distribution – this corresponds to the width that covers approximately 68% of all the distribution. Similarly, the blue line and the blue circle describe the distribution of the Forté grinder.

For now, the app is only intended to be used on OS X computers. But if you are running any other kind of system and know your way around Python, you can always download it directly from GitHub and run it with your own installation of Python 3.

This is an example of how to use the coffee grind size application.

I would like to thank Scott Rao for his excitement when I shared this project idea with him, and for beta testing the software. I would also like to thank Alex Levitt, Mitch Hale, Caleb Fischer, Francisco Quijano and Victor Malherbe for beta testing the software.

Some Strategies to Keep your Coffee Fresh

[Edit October 28 2019: I now strongly recommend against using oxy-sorbs or any oxygen scavenger bags with coffee. I will eventually write a detailed post about this, but it can impart a really bad taste to coffee; for now you can find more information here.]


There are few things more annoying than discovering some of your favorite coffee beans are getting stale and taste much worse than when you first opened the bag. I experimented with various methods to keep coffee beans fresher in the last six months, and I would like to share some of my findings in the form of different options you could adopt.

In short, there are four things you want to keep your coffee away from: oxygen, humidity, heat and UV light. All of those can damage coffee over time. The various tools and approaches described below are therefore designed to protect coffee from one or more of these factors.

Original Packaging

Freshly roasted coffee degases a lot of CO2 for a short amount of time. If it is quickly sealed in a bag with a one-way valve by your roaster, this will contribute to expel some of the oxygen that was initially present in the bag, therefore creating an even better protection against oxygen. When you open the bag for the first time however, all of this CO2 immediately leaves the bag and gets replaced again by the average air composition, with all its oxygen. The coffee does not have that much more CO2 to release anymore, and therefore this newly added oxygen will be free to slowly damage the coffee with oxidation. This effect becomes even more marked when the bag gets almost empty, because then you have more air (and therefore oxygen) in your bag that is free to attack a smaller amount of coffee.

These considerations explain why you can get a great cup from a freshly opened bag roasted a month ago, but within just a week or so after you opened that bag, the taste will quickly degrade unless you take proper care to protect your coffee against oxygen.

Generally, it’s a good idea to open the original bag only when you brew your first cup of coffee with it. You still need to keep the bag away from heat, and it’s good not to shake it too much and store it upright so as to keep its CO2 reserve intact.

Opaque zip-locks with valves

One of the easiest ways to quickly store coffee in a safe place is to use opaque and hermetic zip-lock bag with one-way valves such as these ones. They will protect coffee from humidity, UV light, and also from oxygen up to a point. A lot of roasters already sell their coffee in high quality bags like this, but I find it useful to have a few of them for the moments where I discover a roaster did not add a zip-lock to their bags for example (I’m looking at you with an angry face, all roasters who don’t). Just make sure that you get as much of the air out of the bag every time you close it.

Inert Gases

Bottles of inert gases (typically CO2 and nitrogen) can often be bought in wine stores for about fifteen dollars a bottle. They are a bit hard to order online, but it is worth getting a few of them as a nice addition to zip-lock bags; you can just push the oxygen out of the bag by adding a small amount of inert gases in the bag just before sealing it.

Here’s how I use inert gas bottles: Put the bottle’s straw through the zip-lock, and almost close the zip-lock bag except for a small opening where the straw is. Get most air out of the bag by pressing on it with your other hand, and with your hand still pressed on the bag, give a small 1-second push of inert gases (you can make it 2 seconds if you have a very large and almost empty bag). Immediately remove the straw and close the rest of the zip-lock bag. A typical inert gas bottle will last for a bit more than a hundred uses like that.

You will need to do this every time you open and close the bag however, so this is not a particularly great solution if you constantly brew coffee. In these cases, oxygen pads (more below) are a better solution.

An inert gas bottle.

Vacuum Sealers

Vacuum sealers require a bit more work on your part, but in my opinion they provide one of the best ways to keep your coffee fresh, especially in the long term when combined with other methods. I had amazing coffee vac-sealed months ago with no hint of oxidation whatsoever.

I only tried one vacuum sealer yet, and it turns out that it works pretty well for me. It’s probably not appropriate for industrial use, but I have been using it almost every day for more than three months and I had no issues with it. There are two annoying things about it, but I’m not sure which vacuum sealers don’t have these issues, if any. (1) The plastic bags are way too large and need to be cut, which is a bit more work than I’d like; (2) the vacuum chamber is a bit far from the edge of the sealer, so you always need to leave a bit more than an inch empty in the plastic bag.

Here’s how I recommend using this sealer; take one of the unnecessarily huge plastic bags with a ruler and a pen. Make two marks on the bag at 1/3 and 2/3 of its width (excluding the sealed margins). Do this near the bottom and near the top of the bag. With the ruler, use these marks to draw a vertical line at 1/3 the width and another one at 2/3. Use scissors to cut along only one of these lines (if you cut out both right away, the rest will be more of a hassle). Use the vacuum sealer in heat-seal mode (not vac-seal) to seal both sides that you just cut out. Cut along the second line, and heat-seal both sides again. You now have three thin and long bags; those are much more useable sizes in my opinion, and they will save you plastic in the long term because you will minimize the empty portion of the that the vac sealer forces you to leave.

When you fill a vacuum bag with coffee, I recommend using a relatively large funnel – just make sure the mouth will let beans through without clogging first. As I mentioned earlier, make sure you leave enough space at the top of the bag to seal it properly. I suggest marking what coffee this is and the roast and seal dates at the bottom (not the top) of the bag. The thing that is really neat with this format is that you can easily cut the bag open, weight a single dose out of it, then immediately re-seal it with your vac-sealer. Because you are freeing up more space than you are cutting out every time, you will even be left with a smaller but re-usable bag.

It’s always good to leave your vac-sealed coffee bag on the counter for a dozen minutes after you vac-sealed it, especially when you use a plastic bag for the first time. This will allow you to quickly notice if you didn’t properly heat-seal one of the bags or if it was otherwise damaged, because it will become loose. There is also one thing your vac-seal bags won’t protect against: UV light. It is therefore good precaution to either store them in a dark closet or in an opaque bag.

Make sure you store vac-sealed bags of coffee in a dark place, or in an opaque bag.

Freezing Coffee

There is one device in most people’s houses that is great at long-term preservation: freezers. Keeping coffee in the freezer has sometimes been feared by the coffee community. This is probably mostly true because careless storage in the freezer can quickly destroy your coffee. Remember that humidity is one principal enemy of your coffee; this is one that your freezer alone will not protect against.

To protect your coffee against the humidity and potential odors in your freezer, you simply need to seal it carefully. This is very easy to do with vac-sealed coffee, but I recommend putting vac-sealed bags in a large plastic container, because otherwise it’s easy to poke a hole or tear a bag with the other food you store in the freezer. Cheap zip-locks or plastic containers often do not provide a good seal and are at risk of letting humidity in your bag of coffee. I suggest using slightly more expensive sturdy bags with double zip-locks, or tupperwares with a rubber gasket and clips. You can also use something like the Airscape, but I tend to prefer bags because they take up less space as you use up the coffee. But hey, maybe you don’t store 25 different coffees in your freezer like I do.

There’s another subtlety in using the freezer to store your beans. When you take something cold out of the freezer and leave it in contact with air, the ambient humidity will quickly condense on its cold surface. This means your coffee beans will come in contact with water if you open a sealed bag of coffee that is still cold. This is probably not bad for a dose of coffee you’re about to use, but it is really bad for the rest of coffee you’re about to re-seal. I recommend only using the freezer for medium to long term use: when you decide to drink one of your bags of coffee, just take it out of the freezer a dozen minutes before breaking its seal, and then store it outside the freezer.

If you’re motivated enough to single-dose your coffee in the freezer, you won’t have this problem as much, but vac-sealing them will be really annoying. There is a study showing that cold coffee beans shatter a bit more therefore creating slightly more fines in your grind distribution at typical freezer temperatures, so you might still want to let them thaw a little before grinding them.

I read some baristas refraining from using the freezer because they were afraid that the humidity inside the coffee beans would freeze into crystals. However, I have seen Scott Rao mention that this water is trapped in cellulose cells and cannot crystallize as a consequence – I have not seen studies on this, but my taste buds informed me that coffee vac-sealed and properly stored in the freezer for more than a year still tastes great. I also read that un-freezing and re-freezing coffee is bad; I am not sure why and I never tried, but my guess would be that this is either based on bacterial build up or a gradual weakening of the cellulose cells inside the coffee. One last consideration; I read testimonies about how great ultra-low temperature freezers are for preserving coffee, but those are very expensive and I never tried it.

Oxygen Absorbers

Thanks to Matt Perger who recently shared something about this on Instagram, more recently I decided to use oxygen absorber pads instead of inert gases. They are relatively cheap, can be shipped easily, and they won’t get immediately spoiled every time you open a bag. If you would like to know more technical details on oxygen bags, I recommend reading this page. Here’s a summarized version of useful facts: (1) typical 100cc bags can be used to store up to about a pound of material; (2) it takes several hours for the pad to absorb all oxygen from your bag. Oxygen also won’t attack your coffee extremely fast, so this is good because it also means you don’t have to be in a total rush to seal your bag; (3) when the oxygen pad is completely spent, you can feel through the bag that the materials inside it will are clumpy and crystallized.

If you order some of them, you’ll notice that they come vac-sealed. This should not surprise you, because they would otherwise already be spent (it surprised me for 5 seconds). When you break the package open, I recommend placing them all in a large sealed zip-lock (see above). You can then just open and close the zip-lock every time you need one. Just don’t forget the zip-lock bag open.

My Gold Standard for Storing Coffee

Now that we discussed all the tools that I like to use, here’s my gold standard of how I store coffee that I care about:

  • I leave it in the original bag until I first brew it, unless I want to keep it for long term use, in which case I open it right away.
  • When I open the bag, I transfer it to a few thin vac-sealed bags, each with one oxygen absorber at the bottom.
  • I typically keep one of them in an opaque bag at room temperature and store the rest in a plastic tupperware in the freezer.
  • When I want to use a coffee stored in the freezer, I just transfer it to the opaque bag at least a dozen minutes before I use it (sometimes the night before).
  • When I want to brew coffee, I cut open a room-temperature vac-seal bag, get the dose out, and immediately seal it again.

When I don’t care about a coffee as much, I simply put it in a sealed zip-lock if the original bag lacks it, and put an oxygen absorber pad in the bag. Before closing the bag, you can whisper “you should have been roasted better” in the bag.

A Recipe to Brew High Extraction Coffee with the Siphon

Today I am finally sharing a recipe for the siphon brewer. I will use a bit of technical jargon at times in this blog post. If you encounter a word you’re not familiar with, I recommend you consult Mitch Hale’s glossary.

The siphon method is far from being appropriate for most people’s daily routines, as it is harder to execute correctly, and it takes time and requires more maintenance and cleaning. But the siphon has a really neat advantage: it does not rely on gravity to drive water through the bed of coffee. Instead, air inside the lower chamber is heated, causing it to expand and push water in the upper chamber. When the heat source is interrupted and the air contracts back to normal, this creates a large pressure difference between the lower and upper chambers, and sucks back water through the coffee bed, even if the coffee is ground fine enough to completely clog a V60 brew.

These siphon mechanics open up a very interesting door: you can play with much finer grind sizes and much higher average extraction yields than a V60. The method I want to present you today leverages this to reach much higher extraction yields than what can typically be done with a V60 brew (think of extraction yields 24% and above), while still getting a very clean cup free of oil or fine coffee particles.

I am re-discovering a lot of the coffee stored in my freezer with this recipe; not all of them react very well to these very high extraction yields however. I recommend using this recipe only with coffee beans with very well developed roasts. Otherwise, some woody or astringent tastes may appear much more dominantly than they would in a ~20-22% extraction yield V60. When I receive a new bag of coffee I never tried, I won’t go directly try this siphon recipe on it. Instead, I’ll make a V60 with my usual Rao-style recipe, and if I notice that I can reach higher extraction yields than most other coffee (e.g., 22%), then I will try brewing it with this siphon recipe.

There are a few coffees that yielded great to amazing results with this method for me: The Buufata Konga Ethiopian and the Gesha Village 2018 Wet Processed both roasted by Passenger; the Mamuto AA Kenyan roasted by George Howell; the Kayon Mountain Ethiopian roasted by 49th Parallel; the Kiandu AB Kenyan roasted by Heart; and the Karogoto Kenyan roasted by Tim Wendelboe. All of them produced average extraction yields between 23.2% and 24.6% with this recipe and my Forté grinder, when calculated with the simple percolation equation (I’ll discuss this more below).  However, in my experience very few roasters that I have tried were able to pull amazing roasts several times in a row even when I ordered the same bag of coffee a month later. I’ve only tried a single batch of each of these coffees and they turned out great, but I don’t know whether they will always be great. I also don’t know either of these roasters well enough to make any prediction about this.

I have been trying to use finer grind sizes with the siphon for four months now, with the goal of achieving higher extraction yields, but I was struggling to avoid fines getting in the beverage and to obtain good-tasting brews. As you will see, it turns out that I was failing because I was not being bold enough; there is a valley in grind sizes, from espresso to a bit finer than V60, where coffee fines can sneak through the Hario filter holders. And this led me to believe I could not use a grind size as fine as I hoped with the siphon.

You might be wondering why I would even want to try grinding finer in the first place. To understand the thought process, I recommend reading my post on The Dynamics of Coffee Extraction. It explains why grinding finer will allow you to reach higher average extraction yields and also more even extractions – this is something Matt Perger has been shouting from the rooftops for a while now, but I only recently heard about it.

I have also recently been experimenting Dan Eils’ Vac60 prototype which he generously sent me, and this led me to explore and think about finer grind sizes again. My friend Mitch Hale had also been taunting me with his 26+% extraction yield Turkish brews made with his fantastic EG-1 grinder that everyone is jealous of. All of this led me to try grinding Turkish style for my siphon – Mitch also helped me figure out whether my Forté could actually do it, and turns out it can. These experiments finally allowed me to brew the first high-extraction yield siphon that I really enjoyed, about 60 siphon brews later. If you are a regular siphon user, you may find this recipe somewhat weird or shocking, but please try it before judging 🙂 I especially recommend it for very soluble coffee that doesn’t taste roasty (i.e., try it on great roasts).

The basic idea behind this recipe is that we want to grind as fine as we can and prepare an immersion-style brew similar to Turkish and quickly reach a very high extraction yield, then filter out the oil and coffee fines to get a clean beverage. To achieve this, regular cloth filters are not great because they don’t filter out all the oil. Plus, they are a total nightmare to clean and maintain – they quickly develop a rancid taste, and they can even easily develop mold from their constant contact with water. If you insist on using them, please read the Cloth Filters section at the end of this article, but I honestly have not made a great brew with them even after going through a pack of 10 brand new Hario cloth filters.

Fortunately, paper filters can be used with this recipe, and I find that they produce better coffee. They are also way easier to maintain: you just need to pre-rinse them, brew your coffee, then carefully throw them in the garbage. Unfortunately, the design of the Hario paper filter holder is not too optimal in my opinion. The central screw (WHY ?) allows fines to go through if you grind just a bit finer than V60 brews. But as mentioned earlier, what I recently discovered is that if you grind much finer, you don’t get this problem – the coffee bed becomes much more cohesive (probably because of the surface tension of water) and forms some kind of paste that stops getting around the edges of the filter holder.

One key point of this recipe is that the coffee bed itself is used as a filter, in addition to the paper filter. As long as a small layer of coffee grounds deposit on the paper filter fast enough before the start of the drawdown phase, the rest of the beverage will be filtered out of coffee fines by the bed of coffee itself. The paper filter is still important to absorb coffee oils, an effect that you would not get with a metal filter – I also suspect fines may pass through the metal filter, but I have not tried.

List of Required Material

  • A siphon brewer: I use the Hario Next 5-cup, but I recommend the Hario Technica three-cup if you never brew large batches.
  • A bamboo paddle or any other kind of similar stirring object (ideally food grade and not thermally conductive).
  • The Hario paper filter holder and some paper filters.
  • A heat source: I use the Hario beam heater, but butane heaters should also work. I do not think alcohol heaters would be powerful enough. The “Hario Smart” beam heater works too and is sometimes the only one available, but it is way more expensive.
  • A bead temperature probe. This may seem overkill, but it is not. I find it extremely hard to brew a consistent siphon without it, and without it is also very easy to brew coffee at 180℉ without noticing. A kitchen heat thermometer can work, but it will be much more of a hassle, and much slower because you won’t be able to put the plastic lid on top of the upper chamber to keep the heat in.
  • Some brew water – I like to use the Rao/Perger water recipe. For more detail, see my blog post on brew water.
  • Any clean kettle. If you are extremely patient you could do without by heating water directly with your beam heater or butane heater.
  • A brewing scale. I use the Acaia Pearl scale which is neat because it’s large enough to put the Siphon on, but I’m sure you can get around with other less expensive scales, just make sure you get one precise at 0.1g or better.
  • A timer, unless your scale can act as one.
  • A grinder that can grind extremely fine. I use the Baratza Forté BG grinder which can grind fine enough only when the zero position is well calibrated (more on that below). I suspect the Encore and Virtuoso could also do it, but I don’t know. The more expensive grinders like Mahlkonig EK43 or Lyn Weber’s EG-1 can do it better than my Forté (for a LOT more money), but with the EK43 you will typically needs to align the burrs for that. Going this fine with a manual grinder would certainly be a huge pain when it’s even possible.
  • A small container to hold your dose of coffee beans or ground coffee.
  • Tabbed and bleached Hario V60 filters (not crucial but they can be useful, more information below).
  • Some OxiClean for the occasional maintenance of your siphon glass. Soap can work but it is not as effective.
  • I suggest always keeping a kitchen towel near your brewing space in case the lower chamber of the siphon loosens when it is hot.
  • A bottle brush to clean up the lower chamber of the siphon.
  • A lens blower to help clean up your grinder. This is facultative but it really helps especially when grinding Turkish style.
  • A “not a flamethrower” by the Boring company.

Grind Size

You will want to grind extremely fine for this recipe. The grind size should be finer than espresso and similar to Turkish brews. It should look and feel like flour, and form clumps. You should be able to see your fingerprint if you press a finger on a bunch of ground coffee (see picture below). On my Forté, 1A was not fine enough with its initial calibration so I had to re-zero it with the burr calibration tool. Please follow the Baratza user manual if you do this. Here’s where I set mine: turn the calibration screw until you just very barely start hearing the burrs touching at setting 1M, then use setting 1I (letter i) for this recipe. When the calibration tool is not inserted, I do not hear the burrs touching at 1M, but I do hear them touch at 1I. Please be aware that doing this will mess up all your previously cataloged grind size setups, sorry. The only reason I don’t go finer is because I don’t want to put too much strain on my Forté’s motor; Mitch has been grinding much finer than I do with great results (and higher extraction yields), so I suspect that there is no grind size that is “too fine” for this recipe.

Your grind size should be fine enough that it spontaneously forms clumps.
Your grind size should also be fine enough that it starts retaining low-resolution fingerprints if you press your index finger against the dry coffee. This requires an even finer grind size than the formation of clumps. If you see clearer fingerprints than those on this image, congratulations, your grinder is better aligned than mine ! This is good for you, and you will probably be able to reach higher average extraction yields.

Grinding this fine means that your grinder may retain a lot of ground coffee, depending on its internal structure. For example, my Baratza Forté retains about 1.5 grams with this setting. Because of this, I recommend either grinding about 2 grams of the coffee you are about to use and throwing away what comes out – it’s mostly coffee from the last time you brewed. Another way to do this even better is to turn on the (empty) grinder, move the grind size up to the coarsest setting, and wait for the old coffee to come out. You can then move the grind size back to the desired setting while the grinder is running, and then turn the grinder off.

Preparing the Filter and Workspace

First, make sure you have some un-cluttered space on your counter in front of the beam heater. You’ll need to quickly remove the siphon from the beam heater at some point, and put it down somewhere nearby. If you use the butane burner, it might be easier to move the burner instead, so this might not apply to you. I once had the genius idea to try using a thick cork pot stand and put it on the beam heater right after I turn it off to avoid having to move the siphon at all, but it turns that out even once it’s turned off, the beam heater is crazy hot, and it completely burned the cork stand. I suggest you don’t try this and set your house on fire. If this is your first time using the siphon, I suggest checking that your counter is level; otherwise it could affect channeling in the drawdown phase.

Check that the lower chamber of the siphon is well attached to its stand. I have the Hario Next model, and this part is a little finicky – pushing too much on the upper chamber can cause the lower chamber to come off from the stand, which could be a huge problem when it’s full of hot water. Now that you did that, fill the bottom chamber of the siphon with hot tap water. This will help speed up the brewing process.

Make sure the plastic lid of your siphon (also used as a stand for the upper chamber) is clean and free of water or old coffee. One of the quickest ways to turn your brew to shit is to forget some old coffee at the bottom of the lid and put it on top of your siphon. One way to be sure you don’t do this is to put the lid upside down on the counter after you cleaned it. Also make sure all parts of your siphon are clean and free of coffee oil stains. See the section on clean up and maintenance otherwise.

Mount the paper filter on the filter stand, and gently fold the paper up without straining the edges. Make sure the holes on both sides of the filter holder are aligned by looking through the filter toward a bright source of light. If you can’t see them you can gently wet the filter a little bit. This step is crucial because mis-aligned holes will allow less flow of water and this will increase channeling around the filter holder. Place it in the upper chamber of the siphon – the paper should be folding up, not down.

Pull the hook and put it in place, then make sure the filter stand is centered by looking at the bottom of the siphon chamber and making sure the holes in the filter holder are centered. You can also look sideways and make sure the filter holder is level. You can move it around by holding on the middle pole of the filter holder. Do this before wetting the filter completely to avoid damaging the paper filter when you are installing it in the brew chamber. Run some tap water on the filter to make sure it’s free of paper taste. At this point I recommend putting the upper chamber upside down on your counter until you use it – Don’t use the plastic lid as a stand for now, to ensure the lid is still upside down and entirely clear when you put it on top of the upper brew chamber later on.

The paper filter initially tends to extend downward.
Gently fold the dry paper filter upward with your fingers.
The paper filter should be folding upward in the siphon chamber.
Look from the bottom of the chamber and center the filter holder.
The plastic lid of the Hario siphon also serves as a stand for the upper chamber, but don’t do it for now.

Now determine how much coffee you want to make, as well as your brew ratio. In his Everything but Espresso book, Scott Rao recommends making a batch of coffee that takes up at least 2/3 of your siphon capacity to get a good vacuum during drawdown, and I tend to follow this recommendation. With this method I recommend starting with a ratio 1:17 and go up from there next time (e.g. 1:18) if you find that your brew was too strong. This may be needed for very well developed roasts, which are more easily soluble, or with an extremely well-aligned grinder. For example, you might decide to go with 400g of water and 23.5g of coffee, for a 1:17 ratio. I’ll use these numbers from now on. If your batch is too strong, you can always add some hot brew water to your beverage to lower down the concentration, and it should still taste good. The other way around is not fun, because there is no easy way to increase the concentration of your beverage.

You might notice that you prefer higher concentrations when you brew at very high extraction yields – this seems to be the case for me. I used to prefer TDS concentrations of about 1.3% when I brewed V60s at 19-20% extraction yields, and moved to preferring brews at 1.4% to 1.45% TDS with V60s at 20-22% extraction yields. Now, these siphon brews that get me extraction yields around 24% seem to be more enjoyable at a concentration around 1.5% TDS. Maybe it’s just me 😛

Brewing the Coffee

Boil some of your brew water in a kettle. Empty the warm tap water form the bottom chamber of the siphon, place it on your brew scale and tare, then pour 400g of hot water in it. If you happen to have 1mL glass pipettes, I find it easier and faster to go just a tad over 400g and adjust by removing water with the glass pipette. Place the lower chamber on the heat source and turn the heat up to its maximum level; here I’ll assume you are using a beam heater; I’m not familiar with the butane heater so I’ll let you decide on the exact heat level if that’s your case. You can now preheat the upper chamber a bit by pouring warm tap water on it. This is not required but it will shorten the preheat time.

Place the temperature probe in the bottom chamber, turn on the thermometer and gently put the upper chamber on top without sealing it on. This will allow you to heat up the water for a bit without having it immediately climb up the upper chamber. When the temperature reaches 210℉ or more, remove the temperature probe and place the upper chamber on top to seal it on. Do not press down too much because this could cause the lower chamber to fall down from the stand in which case I wish you luck. Make sure your upper chamber is level; I find it easier to tell when looking at the rubber joint.

It is important not to leave the lower chamber heating up without having anything in contact with the water, whether it is the temperature probe or the tube of the upper chamber. Otherwise, the water could get superheated and “explode” everywhere when you put the upper chamber on. This is caused by the very smooth surface of the siphon – water can go slightly above boiling point without actually boiling if it’s not perturbed in any way and does not have access to a nucleation site (see this Wikipedia article if you want to know more).

Once you sealed the upper chamber, place the temperature probe inside the upper chamber and close it with the plastic lid to get better heat retention. You can now turn the temperature reader on. Now you’ll need to wait for a good 6-8 minutes for the upper chamber to reach 202℉ (94℃) – this will allow you to actually brew at approximately 198℉ (92℃). If just used your siphon, it will be a bit faster; otherwise I find that the temperature stagnates at around ~185℉ (85℃) for a little while as the siphon’s upper chamber glass is sucking up heat and warming up. Take this time to meditate on the idea that the self is an illusion. Also make sure that the brew water is perfectly transparent in the upper chamber, otherwise it means that something was not cleaned up properly and your brew will probably taste like dirt.

You can also use this time to weigh your dose of coffee, set up your grinder and grind the coffee. If you single dose, start the motor before you put the coffee in so that you will be grinding at a uniform motor rotation rate. Single dosing is often recommended against because pop-corning beans get ground coarser than those pushed through the burrs, but in my experience this affects such a small fraction of the dose that it virtually does not affect the particle size distribution (this will be a future blog post).

Make sure your small coffee container is perfectly dry, otherwise ground coffee might stick in it and this will be very annoying. Weigh the exact dose of ground coffee in the container. You can wait a bit to grind if you are afraid that the coffee loses freshness, but I was unable to taste a difference even when I ground right when I turned the beam heater on. Just put something on top of your ground coffee container to limit contact with air. I like to put the grounds in a container smaller than the width of the upper siphon chamber to help pouring it more quickly and precisely later on. Just make sure you use a clean container. I also like to use a tea spoon to transfer ground coffee from my Forté’s bin to the container to avoid spilling coffee.

The bead-type temperature probe allows to accurately measure the upper chamber of the siphon with the plastic lid on. This will allow you to brew more precisely and reach the proper temperature more quickly.
Bubbles will form because of small gaps at the edges and the center of the paper filter holder – this is normal, and surprisingly coffee fines won’t be able to sneak through these same gaps if you grind fine enough.

When the temperature reaches 202℉ (94℃), it is time to start brewing. If you missed this window, turn off the heat (leave the plastic lid on to avoid evaporation) and wait for the temperature to go back to about 195℉ (91℃) then turn the heat back on. If you see temperature going up so fast that you will probably miss the window, it’s ok to turn down the heat to approximately 1/3 of the maximum while you finish your preparatives, and then turn it back on to maximum heat. This will cause the temperature to go up much more slowly, without losing enough pressure for the water to fall back in the bottom chamber.

Once you reached 202℉ (94℃), lower down heat to approximately 2/3 of the maximum (on my Hario beam heater this is at the logo with two flames), and immediately remove the lid. Remove the temperature probe now if you don’t want to have to clean it up. Start your timer and quickly put the coffee in the upper chamber. To minimize spilling, place your coffee container centered straight above the siphon, turn it upside down and gently tap it with your other hand (this takes me approximately 4 seconds). Make sure that no grounds are stuck in the container, it’s worth tapping a bit more vigorously if they stick. Use the bamboo paddle to vigorously stir in up-down and left-right linear motions to create a lot of turbulence and maximize extraction, until the timer hits 0:15. This is a good time to hum some Fleshgod Apocalypse.

I find that holding the bamboo paddle straight vertically and moving your arm in a back and forth motion, rather than keeping your hand in the middle and paddling with your wrist, will minimize splatter on the glass walls. This should allow you to quickly break down any clump of dry coffee. If some grounds stick to the glass walls, try to quickly drag them back in. End the initial stirring phase with a very short and vigorous rotation motion (e.g. 1 turn) when the timer hits 0:15.

I also tried using a kitchen whisk instead of a bamboo paddle, but I was not satisfied with the results. The width of the paddle makes it easier to induce a strong flow in the slurry, which creates a lot of turbulence – I trust turbulence more than the many branches of a whisk to break down clumps of dry coffee.

I don’t think you need to be too obsessed about the repeatability of your stir, because this recipe aims to quickly reach very high extraction yields, which also quickly saturates the concentration of the slurry. As a result, extraction will become very slow after the first few seconds of immersion, so differences in how much you stir will only marginally affect your final extraction, as long as you break all clumps of dry coffee. Mitch and I were able to produce subsequent brews at the same concentration (down to 0.01%) with this method, when we used the same coffee beans.

When the timer hits 0:35 (yes, just 20 seconds later), turn off the heater and very carefully remove the siphon from the beam heater and put it on the counter. You don’t want to impart any acceleration that could agitate the coffee bed. You can make the drawdown phase faster by wetting a rag with cold water and immediately wrapping it around the bottom siphon chamber (I recommend wetting it during the 20 seconds wait and already have it in your hand). This is especially useful if you are brewing smaller batches. If you do this, you will need to remove the rag as soon as it feels hot because at that point it’s working against you by insulating the siphon chamber from cooler ambient air. Whether you decided to use a cold rag or not, immediately start inducing a slightly vigorous rotation motion in the slurry with the bamboo paddle. I do something like 5 full rotations in about 3 seconds total. Don’t put the paddle too deep because you don’t want to agitate the coffee bed that started depositing at the bottom; I put it about half the slurry deep. Note your total brew time when the beverage in the lower chamber starts bubbling heavily. Try to have a total brew time shorter than 3:00.

Scott Rao recommends that the shape of the coffee bed should resemble a slight parabola at the end of the drawdown, which goes slightly above the central pole of the filter holder. The reason for this is to avoid channeling and ensure an even extraction. This recipe allows to reach very high extraction yields during the immersion phase (before drawdown), so I think that this requirement a bit is less critical. I tried measuring the concentration of the upper chamber (with syringe filters and the VST refractometer) immediately before drawdown and I obtained exactly the same concentration as the final beverage, down to a precision of 0.01%. Extreme levels of channeling could lead to the paper filter breaking or fines passing around the filter holder in the beverage, but in my experience this did not happen even when the coffee bed was flat.

Scott convinced me that I should still care about channeling despite these considerations, and after a bit of experimentation I did produce some relatively astringent brews when channeling was significant, so I still recommend that you care about it too. Keep in mind that it is much harder to obtain a nice dome-shaped coffee bed with an extremely fine grind, in part because the drawdown phase takes more time, but I also suspect that the bed crumbles more easily. If your coffee bed is too flat, it means you didn’t cause rotate the slurry enough with the paddle, or you rotated it too early before drawdown. If the the center of the coffee bed is too high and is shaped like a dome, it means that you rotated too much.

The ideal shape of the coffee bed (in red) and my closest approach with such a fine grind size. As you can see, the bed cracked on its sides at the very end of drawdown.
This coffee bed has too much curvature and resembles a dome, indicating that I applied too much rotation with the paddle, and that the percolation phase channeled. You know you had channeling if the depth of the coffee bed is almost zero along the edges of your siphon chamber.

Once the drawdown phase is over, carefully remove the upper chamber (it will be hot), and place it upright in the siphon plastic lid, which also serves as a stand for the upper chamber. Once the foam around the coffee bed disappears, look at it from above; a non uniform color would indicate an uneven extraction due to channeling. The coffee bed will often crack, this is normal with such a fine grind.

A view of the coffee bed from above. The color of the coffee grounds is uniform, except for the light reflections caused by the glass walls.

Brews produced with the siphon are initially much hotter than most other brew methods. It will be hard to taste all the subtleties of the coffee when it is still very hot, and while it looks, the bottom chamber of the siphon won’t allow the coffee to cool down very quickly. For this reason, I like to pour the coffee out into a different vessel. You will automatically lose around 10℉ (5℃) when pouring out the coffee this way. If you have the Melodrip, you can pour your coffee through it to get it to an enjoyable temperature faster. James Hoffmann suggests to do this promptly, because the very high temperature may actually degrade the coffee flavors after a while. I never tried blind tasting to confirm this, but I follow the recommendation because it’s an easy thing to do and I prefer drinking coffee when it’s a bit cooler anyway.

If you look at your siphon beverage from under a bright light, you should see a clear beverage free of fines. The shades in this image are due to a deformed image of the lamp behind it.

More Beverage Clarity

I found that sometimes, these siphon brews left a small bit of coffee oil in the beverage, which probably passed through the edges of the filter mechanism. This is a small amount that is not always obvious to taste, but I found that filtering the siphon brew again with a pre-rinsed V60 paper filter will remove any potential oil left in there, so I recommend it if you are not low on paper filters.

To do this, simply put a V60 paper filter in any type of V60, pre-rinse it and pour the siphon beverage through it. I try to pour it uniformly across the walls of the V60 paper to use as much paper surface as I can, and absorb as much oil as possible. This is one rare occurrence where you don’t need to care about what material the V60 is made of, because it’s not actually a bad thing to cool down the beverage a bit more.

If you want to measure your beverage weight to get a more accurate measurement of your average extraction yield (see below for more details), this is a great moment to do it. Simply place your vessel and V60 on your brew scale, tare it, and pour the coffee. Just make sure you note the weight measurement before removing the V60, because you tared the scale with the V60 on.

Filtering the brew a second time with a pre-rinsed V60 paper filter will ensure that no coffee oil remains in the beverage. Pouring the brew on the sides of the V60 walls will allow it to absorb more oil.
The V60 filter will become slightly stained by coffee oils, but as you can see no coffee fines are visible on the paper filter.

Summary of the Brew Steps

Here is a short summary of the recipe detailed above. Here, I will assume that you are using the 5-cup sized siphon to brew an approximately 400g beverage and that you are brewing with a 1:17 ratio.

  • Boil more than 400g of brew water with a kettle.
  • Mount the paper filter on the filter holder.
  • Install the filter holder in the upper siphon chamber.
  • Make sure the paper filter is centered.
  • Rinse the paper filter with tap water.
  • Place the lower siphon chamber on your brew scale and tare.
  • Pour 400g hot water in the lower siphon chamber.
  • Place the lower siphon chamber on the beam heater and turn it on at maximum heat.
  • Immediately place the upper chamber on to seal it. Don’t press down too hard. Make sure it’s level.
  • Place the thermometer probe in the upper chamber and turn the thermometer on.
  • Make sure the plastic lead is dry and clean and place it on the upper chamber.
  • Weight about 25g of beans (or 23.5g plus whatever your grinder retains).
  • Grind the beans, weigh a dose of exactly 23.5g, and cover the grounds.
  • Wait for the temperature to reach 202℉ (94℃).
  • Lower the heat source temperature to 2/3 of the maximum.
  • Remove the plastic lid and temperature probe.
  • Start the timer and put in the coffee dose.
  • Stir vigorously in linear motions until 0:15 then make one vigorous rotation.
  • Wait 20 seconds. Prepare a rag wetted with cold water and keep it in your hand.
  • At 0:35, turn off the heat source.
  • Immediately and gently remove the siphon from the beam heater.
  • Place the cold wet rag around the lower siphon chamber.
  • Immediately impart a slightly vigorous rotation (5 turns in 3 seconds) while placing the paddle approximately half as deep as the slurry.
  • At any point where the rag becomes hot, remove it.
  • Note the drawdown time when the beverage starts bubbling. Aim for less than 3 minutes.
  • Inspect the shape and color of the coffee bed.
  • Facultative: pre-rinse a V60 paper filter and filter the beverage through it.
  • Facultative: use the Melodrip if you want to cool down your brew faster.
The siphon brewer in all its hellish might.

Clean up and Maintenance of the Siphon

Cleaning up the siphon takes a bit more time than other brew methods. I suggest first unhooking the filter holder while the upper chamber is upright, then place yourself above the sink, reach for the central pole of the filter holder with your other arm and gently lean the chamber on its side until it is upside down. Make sure you are holding the filter holder while you do this, and carefully remove it. Be careful as the coffee may still be hot. The filter holder and coffee bed are a bit heavy, and this will avoid damaging the glass walls of the siphon chamber. Rinse the filter holder and throw the paper filter in the thrash. Rinse both siphon chambers, the bamboo paddle and the plastic lid thoroughly, and leave them to dry. It’s good to wipe your beam heater clean too.

From time to time, I recommend cleaning up the glass parts (both chambers) of the siphon with a single drop of soap and a wet cloth. Make sure you rinse the soap thoroughly. You will need a bottle brush to clean up the inside of the lower chamber.

More rarely, or if you need a very thorough clean up of your siphon, you can put a solution of OxiClean (up to Line 1 of the provided spoon) in 500g of water in the lower chamber, and heat it up with the upper chamber attached and sealed. Do not put the bamboo paddle or filter holder in when you do this. Wait for a few minutes, then throw away the water and rinse all parts very thoroughly.

Calculating the Extraction Yield of your Beverage

The typical immersion equation (concentration times water-to-dose ratio) will not give you accurate results at all when calculating the extraction yield of a siphon beverage, and will tend to over-state your extraction yield by as much as ~2%. For more details about this, I recommend reading my blog post about how to calculate extraction yield for different brew methods.

The siphon method is special because the pressure differential during drawdown sucks out most of the interstitial water from the spent coffee bed. In the brews I have experimented with, the liquid retained ratio (mass of retained water divided by mass of coffee dose) was between 1.3 and 1.5, which is lower than the usual liquid retained ratio (about 2.0) for V60 brews. As a consequence, it will be more accurate to weight your beverage and simply use the percolation equation for extraction yields (detailed in my blog post on extraction). This assumes that all of the water retained in the coffee bed is absorbed in coffee cells rather than interstitial, and therefore does not participate to extraction. A slightly more precise way would be to assume that the coffee bed absorb its own weight in water (fabs = 1), that your slurry concentration is the same as your beverage concentration, and enter your beverage weight, water weight and dose in Mitch Hales’ online extraction yield calculator.

If you have a refractometer and want to verify whether coffee fines made it to your brew independent of your palate (fines would flatten the taste and leave a silky feeling on your tongue), you can use VST syringe filters and compare your concentration with or without using the syringe filters. If you followed these steps properly and have a well aligned grinder, both readings should be within 0.01% of each other. I highly recommend reading Mitch Hale’s post on how to measure extraction yields accurately.

This method allowed me to reach extraction yields up to 24.6% on a few coffees now, and I suspect I may be able to reach even higher extractions with very well developed roasts. Mitch has reached crazy extraction yields of 26% with his Turkish brews but I suspect this has more to do with his EG-1 grinder producing less “boulders” (the term is very relative here).

I tried this method on about 8 different coffee beans now, with really great results. Contrary to my expectations, I brewed an amazing Gesha Village that retained a lot of its floral and honey notes, and made great Kenyans and Ethiopians too. I did however try one particularly under-developed roast and it tasted awful and astringent. I suspect that this brew method will be best when you use well-roasted, high-quality beans, and it’s possible it won’t play well with some types of coffee. As Mitch put it, “you should use this when you actually want to extract everything from the beans”.

Cloth Filters

This is an adaptation of this comic at pbfcomics.com, reproduced with permission of the author.

For a reason that escapes me, siphons are traditionally sold with cloth filters. I have found that brews I made with cloth filters tasted less good than those I made with paper filters, even if I used a brand new clean and well-rinsed cloth filter, and post-filtered the brew with a V60 paper filter. However, the worst part about cloth filters is the rancid taste that they very quickly develop, even after just one brew.

If you insist on using them, here are some recommendations for you. When you install them on the filter holder, always do a simple loop knot, not a double one, otherwise you will hate yourself later on. Also buy a bunch of them, at least 10. After every brew, immediately clean up the top chamber of the siphon – leaving the coffee bed on will stain the filter more. Clean up as much of the coffee as you can by running tap water in the upper siphon chamber before you remove the filter holder, otherwise coffee fines could get stuck in the string seams of the filter.

Immediately wash the filter thoroughly under hot tap water and rub it gently with the palm of your hand until it looks white. Twist out as much water out as you can, and immediately store it in a sealed plastic container with something that absorbs humidity (raw rice would work). Place the plastic container in the freezer. You can keep a single plastic container filled with rice with all of your dirty cloth filters.

The only way I found to get the rancid taste off from cloth filters is to boil them with unscented, dye-free OxiClean (yellow label) after every brew. This is why I suggest doing this in batches once you accumulated at least a couple dirty filters. Once you have accumulated enough dirty filters, take the plastic container out of the freezer and let it thaw for the rice to separate from the cloth. Shake down the filters and throw away and replace the rice in your plastic container. Boil all filters in a solution of OxiClean and water (follow the package recommendations for the dose; fill spoon to line 1 per approx. 500 mL water) in a large pot. I recommend putting a lid on the pot and turning on your stovetop fan to the maximum, because this stuff stinks.

You can dry tumble your freshly washed cloth filters in a meshed cloth bag like this one.

Boil the filters for about 15 minutes, or until all filters look white, stirring occasionally. Throw away the dirty water, and rinse the filters with cold water. If they do not look perfectly white, do another OxiClean boil and rinse them again. Put them back in the pot with clean water and boil them again for 15 minutes, stirring occasionally. Do this again if they still smell like OxiClean; using a larger pot with more water will make this more efficient. When they don’t smell bad anymore, place them in a strainer and rinse them with cold water for a minute or so. Twist the water out of each filter and place them back in your plastic rice container in the freezer. If you don’t want to wait until you have no filters left before cleaning them, you can use two plastic containers, one for dirty filters and one for clean ones. Another option is to dry your freshly cleaned cloth filters in the tumbler. I tried placing the filters in a meshed cloth bag, similar to what you would use to buy fruits at the grocery store.

Welcome to Hell.

Some Acknowledgements

I would like to thank Mitch Hale for useful discussions and Dan Eils, who re-invigorated my interest in fine grind vacuum brews by generously sending me his Vac60 prototype. Thanks to Scott Rao for providing a lot of help to minimize channeling with this method. Thanks to Victor Malherbe for suggesting the use of a lens blower to clean up coffee grounds. I’d also like to thank Matt Perger and Barista Hustle for sharing a considerable amount of their knowledge about coffee extraction in general. Without this knowledge, I would not have cared about grinding finer in the first place.