Questions & Answers

Photo by Kathy Gagné

This page groups some questions that readers have sent me, either through blog post comments, Patreon, Reddit, Instagram or by email, and the answers that I gave them. I won’t list here all the questions that I receive (that would be insane), but I’ll try to gather those that I think might be useful to the most people.

Reminder: as an Amazon Associate I earn small commissions from qualifying purchases made through some of the links below. Other than these Amazon Affiliate links, I do not receive any benefits from other third party vendors listed below; those are simply the products I chose myself.

Total Hardness and Alkalinity of Bottled Water

Question: I recently went away for the holidays, and since then my V60 brews have become terrible. I travelled with my scale, grinder, V60 etc and the only new variable is the water. I have tried two different kinds of bottled water with poor results. I want to add minerals to the bottled water, but I cannot figure out the KH (total alkalinity), GH (total hardness), etc. from the labels so that I can use your excel document correctly.

Answer: Water bottles give you the mineral concentrations in mg/L, and you can convert those to “ppm as CaCO3” units with my bottled waters spreadsheet. The HCO3 concentration of the bottle will tell you about its KH, and the Mg and Ca concentrations will tell you about its GH. First convert them from mg/L to “ppm as CaCO3”, them add them together to get the total hardness.

Brewing with Smaller Doses

Question: Can one make an excellent V60 with only 15 grams of coffee?

Answer: I think so yes, but it seems more finicky than 22 grams doses. I have only tried 2-3 brews so far and they were not great, but my intuition is that you would need to use less agitation (pour from lower, or even use a Melodrip) and swirl very gently. I have friends that use small doses who don’t swirl at all, because they tell me it almost always destroys their brews. I will post about it once I have experimented enough with smaller doses.

Frozen Hoppers

Question: Daily Coffee News recently posted an article discussing Proud Mary Coffee’s approach to freezing green and roasted coffee. According to Proud Mary, grinding frozen coffee beans results in a more uniform grind size distribution. Barista Hustle have a white paper article about grinding with beans at different temperatures. If I understand that white paper correctly, its results suggest the opposite, that grinding with beans at temperatures above room temperature (not frozen) actually results in a more uniform grind size distribution. Am I understanding this correctly? This has always been a fun and interesting aspect of coffee for me, so I would love your input!

Answer: Grinding cold beans will make them shatter more, and therefore generate more fines. Most particle size distributions (PSDs) are double-peaked, with a coarser peak that corresponds to cutting and a second one that corresponds to shattering. If you grind espresso very fine in a way that both peaks are very close to each other, you may gain in uniformity by increasing the shattering peak; that’s what the Nature report seemed to demonstrate although in a super vague way in my opinion. Matt Perger told me espresso shots tasted better in his experience when grinding cold (and dialed in appropriately).

For V60 or any other methods, the story is very different because increasing the shatter peak will make your PSD less uniform overall. Scott Rao talked about this in one of his blog posts. I haven’t tried dialing in V60 with cold beans, but I did start an experiment with 60°C beans; I had to grind much finer, but the result was weird, I think I was losing a ton of aromas when grinding the beans warm. I didn’t get an obvious gain in extraction yield but I ran out of coffee before it was dialed in properly. I might be able to obtain laser diffraction PSDs for beans at various temperatures in the future, if so I’ll definitely make a blog post about it.

Another consideration from the Illy book is that apparently coffee oils play a role in dissolving some aromatic compounds and helping to prevent their evaporation before they end up in the espresso cup. This is most important for espresso because most oil is filtered out with drip coffee. If you reduce the temperature of the beans, the oils (as everything else) will become a worse solvent and will let go of some of the aromatics it had dissolved, meaning that in the case of espresso you *may* get less aromas that make it all the way to the cup. This is a bit counter-intuitive, because it runs reversed to the usual trend where warmer stuff evaporates faster. I don’t know which effect is more important; maybe cooling down is still good for aromas because they evaporate more slowly even though they aren’t as well dissolved in the oils.

Coming back to Proud Mary; their focus is probably espresso as makes most sense for coffee shops. If that’s the case, then grinding cold beans seems like a good idea both for quality and repeatability – keeping the beans cold will also prevent the grinder from heating as much and that means they won’t need to shift their dial-in mid day. One worry I would have is the condensation that may form on the beans, especially when opening the freezer to fill the hoppers. It’s possible that with enough production that won’t matter, for example if they run through a full hopper in less than a day. It’s definitely interesting, and I’d love to taste the difference.

Chemex and Ethiopian Coffee

Question: I started out with a Chemex, and soon realized that Ethiopians almost always taste terrible on it. So that begs the question: why? I have a few ideas. 1) Bad filters, although this would not make total sense since I’ve bought the same filters and it happens with each box. 2) Brittle beans, that is that Ethiopians tend to be more brittle and thus fracture more so than most, resulting in lots of powder. 3) typical Ethiopian peaberries. The small beans don’t do great when grinded, also resulting in powder.  What are your thoughts?

Answer: I’m pretty convinced the answer is #2; if you go on my Instagram page, I have a recent post showing that Ethiopians draw down much slower than normal. I suspect this is due to beans being harder and shattering more in a grinder. The Chemex will be sensitive to that because it doesn’t have great flow to start with, because the filter sticks to the chemex walls. Here are some possible suggestions if you want to stick with the Chemex when brewing Ethiopian beans: (1) Grind Ethiopians a bit coarser, (2) Put chopsticks between the chemex walls and the filter, or even put a V60 in your chemex lol.

Calculating the Extraction Yield of Cold Brew

Question: I’ve been reading your posts about extraction and the differences between percolation and immersion and a question came up to me. It happens that I’ve been playing around with cold drips and cold brews where ratios are quite different and far from the 1:15 to 1:17 “classical” ratio for the majority of methods using hot water. I guess all the explanation above as well as the formulas apply in the same way for cold or hot extractions… am I right? The thing is… what if I end up with a concentrate drink of about let’s say 3.5 to 4% TDS, then dilute to a Ready to Drink (RTD) beverage… should I be doing the math for the concentrate rather than the RTD? If so… how would I use the chart when my ratios are in the range of 1:4 to 1:7? Thanks in advance for giving some light on this!

Answer: If you add bypass water to transform your concentrate to a RTD, it should not be included in the calculations when you want to determine your extraction yield. Therefore, extraction yield should be calculated directly from the mass, concentration etc. of your concentrate, before adding any water to it. Adding water will lower its TDS, but it won’t have any effect on the average extraction yield. It will be hard to use the charts I provided with ratios of 1:4 to 1:7, because they were made for filter-type concentration beverages. Your recipes will be more similar to espresso, but kind of in between. I suggest you use the equations instead. The chart descriptives (bitter etc.) obviously won’t apply to your TDS because you will change it before drinking. I suspect the extraction yields that do taste good should be similar (anywhere between ~19 and 24% depending on the coffee and roast).

Pasteurizing Cold Brew

Question: I have being brewing cold brew for two years now. I found a simple defect about cold brew, it doesn’t last too much before it gets old. So, I have being pasteurizing my cold brew and clients didn’t even felt the difference about taste and I’m still on lab samples but I wanted to ask you what you think about that ? What you recommend ?

Answer: Yes I think it’s super important to pasteurize cold brew if you don’t immediately consume it, especially if you distribute it to other people. I highly recommend you listen to this particular episode of the Map it Forward podcast. It features a food scientist who explains a lot of the science behind why you need to pasteurize cold brew coffee. Cold brew is a method that doesn’t kill off all bacteria with hot water, so this is why it goes bad much faster than hot brews.

About the Number of Pours in a V60

Question: For V60 would you please explain the advantage of two pours over one continuous pour?

Answer: Here are the advantages that I think happen with two pours:
1) A more agressive extraction: you have a second stage where the water is clear again, providing a more efficient solvent.
2) Less bypass water. There is always some bypass water going through the sides of the V60 around the coffee bed, but I don’t know yet how fast this flow is. Depending on how fast it is, having just one pour might cause a bit more bypass water than two pours. I haven’t experimented enough to be sure about this.

From the few slurry temperature logs I have taken, the slurry temperature seems to stabilize after a dozen seconds where the water level is above the level of dry coffee grounds, so I don’t think that the two-pours method has a slurry temperature noticeably lower than a long continuous pour, but this can certainly become an issue with more than 2 pours, especially if you want until you see the coffee bed between each pour. Some might enjoy coffee brewed with lower slurry temperatures, but I don’t seem to.

One possible advantage of the continuous pour is that a higher column of water in the V60 applies more downward pressure and makes the water flow faster through the coffee bed. This generally seems to be a good thing, both theoretically and in practice: I seem to enjoy brews most when I can keep the flow of water through the V60 above 1 gram/second. I will eventually give a proper go to James Hoffman’s continuous pour method and report my findings.

Temperature Stability and Flavor Profile

Question: I’ve always understood that temperature should remain stable during the brewing process, but what is the influence of temperature changes over time? Do swings in the temperature during the brewing process influence extraction or flavor profile? Is there a window where variations in slurry temperature essential have the same results? Perhaps +/- 3 degrees?

Answer: An unstable temperature will just extract different flavor profiles at different moments of the brew, so yes it will affect the end beverage. At any given moment during the brew, the extraction depends on temperature T, but not on its rate of change dT/dt (where t is time). But if you add up all extracted chemicals at all points in time, you get a different beverage if you had a stable temperature vs unstable temperature. I have no idea if the best results are produced by a stable temperature, but I wouldn’t be surprised if that was the case. I also don’t know what window of temperature variation would be “acceptable”, I’m hoping we’ll eventually learn about all of these things.

Tomato Coffee

Question: Is a savory tomato flavor always a fault in your mind? I’ve had some that change with temperature and I can’t say it’s always been bad for enjoyment. This post from Sump called “Savory Flavors in Coffee” explains it better.

Answer: Some people that know more than me about it think that tomato/savory is mostly a roast defect, and in my experience I did enjoy some of them, when the tomato/savory was subtle, but I always ended up getting tired of that taste after a cup or two. There’s something about it that ends up being a bit overwhelming, contrary to real tomatoes. It also seems that when the tomato or savory taste becomes strong, it’s at the expense of cup complexity, probably because it prevents from tasting the rest. So, yes I consider it mostly as a defect, but getting hints of it as part of a complex profile is fine.

Crafting Brew Water with Different Hydrous Forms

Question: I checked your Google sheet but couldn’t find a conversion factor for using anhydrous Magnesium Sulfate instead of heptahydrate. Do I use the ratio of molar masses (i.e. by doing anhydrous/heptahydrate x heptahydrate mass) to calculate the correct mass? I.e. 120.366 g/mol divided by 246.47 g/mol multiplied by 8.75g = 4.27g?

Answer: You are right, you just want to keep the number of Mg atoms the same, regardless of how many water molecules are hanging out with them. I added the anhydrous MgSO4 weight as column M.

Liquid Retained Ratio in Pressurized Brews

Question: What happens to the water retained in a spent coffee bed if you squeeze the spent ground by applying, say, 2 bars worth of pressure to get the interstitial fluid out?

Answer: This is pretty much what happens with Aeropress or a Buchner funnel and a small pump. From the couple tests I have done, it seems to reduce the retained water to a ~1:1 ratio. My interpretation is that typical ~2:1 retained ratios are made up of about 1:1 interstitial water removable by pressure, and 1:1 absorbed water not easily removable by pressure.

How to Minimize Astringency

Question: How do you minimize astringency in your V60 brews? I think you have recommended doing the Rao spin only 1-2 times and pour slowly (~5 g/s). Also, one can grind coarser, but sometimes this takes away from the flavor of the brew. On a side note: I’ve noticed I get more astringency with Ethiopian/African coffees (with my Baratza Forte) likely due to the more fines produced and longer drawdown times. How do you combat this without sacrificing flavor?

Answer: There are a couple ways to reduce astringency; the main one is to grind coarser, but as you mention you can lose some brightness of flavors. Using a grinder with a more uniform particle distribution helped to grind finer without astringency in my experience. Depending on your grinder and the coffee, you might need to swirl very gently. For example, conical burrs or ethiopian coffee will produce a lot of fines and you’ll need to swirl much more gently to avoid filter clogging. If you see that your brew slows down a lot near the end, try swirling gentler, and if that’s not enough try also pouring from lower down with your kettle. If that’s still not enough, you might be forced to grind coarser, or go down the rabbit hole of using smaller doses (those are harder to do right in my experience, and require less agitation in general).

Aging Issues with Dry Minerals

Question: I made the 200mL Rao/Perger recipe again of which I have made numerous times. This time around the mineral concentrate did not really offgas after I poured in boiling distilled water. This offgassing has seem to wane each time I make concentrate (every few weeks). Could this be a sign of some of my minerals reacting in storage (i.e. “going bad”)? Currently they are in ziplock bags within ziplock bags.

Answer: That is super weird ! I guess it’s possible, but to be honest I don’t know. I would think the effect would be humidity getting in some of the minerals which would artificially make their weight larger, resulting in lower KH & GH in your recipes. The only way to know is to measure it with an aquarium titration kit !

Scale and Corrosion

Question: Can you confirm it will be safe in an espresso machine’s stainless steel boiler, especially in terms of corrosion? If not, what water would you recommend?

Answer: I have not yet included corrosion or scale calculations, so I would recommend using this water crafter by David Seng to verify that. La Marzocco also have a Langelier Saturation Index calculator that could help you.

Measuring Tap Water Composition

Question: My local water report seems too vague to be helpful. It provides a range and maximum values for calcium etc. any suggestions for using this information with your calculator?

Answer: I’d recommend getting an aquarium titration kit for GH & KH at a local aquarium store. This will get you the total hardness and alkalinity. They are hard to shop online because they contain dangerous chemicals.

Turbulence and Astringency

Question: This Barista Hustle blog post on channeling seems to suggest it’s the turbulence that causes increased extraction rate of tannins, instead flow uniformity. What are your thoughts ?

Answer: I’m very skeptical of that 🙂 turbulence (typically caused by a fast flow when water hits the slurry) ensures a much faster extraction, but it also ensures an extremely even extraction, so unless you over-extract everything, I don’t think it causes astringency. To the contrary, making extraction more even should allow you to reach a higher average extraction yield without encountering local over extraction anywhere. From my experience, turbulence can be a great tool.

V Shaped Brewers and Extraction Evenness

Question: Do you think the cone-shaped design of V60 cause uneven extraction simply because the ground at the bottom will have more water passing through it then the ground on top?

Answer: This is a very insightful question, but on the contrary I think it is better than a cylinder-shaped brewer because it partly compensates for the bottom grounds always encountering more concentrated water, which is a less potent solvent. Therefore the V shape is a way to compensate this by having more water pass through the bottom grounds.

Bypass in V60 Brews

Question: You mentioned on your Telegram that the higher the water level, the more chance of bypass water passing between the filter and the V60. So wouldn’t James Hoffman’s method result in more bypass?

Answer: When I mentioned this on Telegram, I was in the middle of an experiment which results I had not fully digested yet. I’m still not fully happy with my understanding of bypass water, and I’m confident the Krazy glue clogging experiment doesn’t prove that bypass happens a lot. I’m still not sure how much bypass happens during a normal V60 brew, and I suspect it’s not a very big amount – I’m still thinking about ways to measure bypass better. In other words, I’m not too worried about Hoffman’s method causing a lot of bypass, at least for now.

V60 Filter Rinsing Consistency

Question: Do you pour the same amount of tap water and hot water each time to rinse the filter?

Answer: No I don’t. As long as you pour enough for the filter to be wet, I don’t think a high level of consistency is needed for that step.

Aeropress Pressure

Question: Do you think the pressure applied on an Aeropress is sufficient to impact the flow uniformity and extraction yield?

Answer: Yes I think it does have an impact. A friend or mine (Alex Levitt) says that pressing more gently also makes the brews less turbid. I have yet to verify that, but the same flow vs extraction yield uniformity considerations should apply also for Aeropress, which means applying too little pressure might hurt extraction evenness. However, the first immersion stage already jumpstarted extraction, and the percolation phase happens with concentrated water and partly spent coffee grounds. This means that a lot less extraction must be occurring during the percolation phase, and the effect of flow on extraction evenness might be less dramatic than the case of a V60.

Kettle Flow and Flow Rate

Question: Will the turbulence from a high kettle flow disturb the coffee bed and affect its flow rate and uniformity ?

Answer: Turbulence from the kettle will help extraction, but also temporarily make the coffee bed shallower, which will result in (1) a faster flow (see Darcy’s law) and (2) less filtration during that short time. Having a taller water column on top of the coffee bed (even if you pour gently with a Melodrip and close to the coffee bed, but fast) is also a way to get more flow without necessarily having more agitation. The impact of having a temporarily shallower coffee bed has its positive and negative sides, which are comparable to using a smaller dose of coffee.

Blind Cupping with Four Samples

Question: There’s a slightly different triangle test that’s quite convenient, which is to have four cups instead of three, consisting of two sets of two. The exercise is to pair the two sets of two. This is practical because it is easy to set up for espresso if you use a spouted portafilter to prepare two cups from one basket (assuming that they pour evenly). If you are tasting brewed coffee, you can split one brew into two cups. Do the stats presented in your post work out the same for this? If you pick out any one cup randomly, then you are left with a regular triangle test.

Answer: I think the two/two case is statistically the same as a triangulation, because you know in advance there are two cups of each type of coffee. Imagine it like this; first choose any cup randomly and set it apart. Then you need to do a triangulation with the remaining three, and you automatically know that the cup you set apart is the same coffee as the intruder in your triangulation. In other words, you can use the same web tool and enter the data as if you had 3 cups with 1 outlier, and enter the amount of “success” and “fail” results to get a probability even if you’re doing a two/two pairing. It would only be a different problem if you didn’t know in advance how many cups there are of each type of coffee.

Flattening the Coffee Bed with Vibration

Question: What about lightly vibrating the grounds mechanically during brewing (or at least during the bloom phase)? This might close the larger channels and move particles to more positions in the flow path, causing greater (or more even) extraction.

Answer: I threw this idea at Scott a while ago and he said that when he tried it it caused a lot of fines migration. I have not tried it myself, but the usefulness of doing this might also depend on how much fines a grinder generates.

Crafted Brew Water is Turbid

Question: I made the suggested Rao/Perger mineral concentrate and it precipitated as you pointed out would occur. However, it seems the precipitate remains even when the concentrate is added to distilled water (I can see turbidity when held up to the light). Is this normal?

Answer: I’ve had this happen to a couple persons now. First, make sure that you shook the brew water well and gave it at least 15 minutes for it to dissolve the concentrate entirely. If the issue persists, my best working hypothesis is that one of the ingredients you bought is contaminated with something that’s hard to dissolve. For pour over it probably won’t have any effect, except that your weight for that particular ingredient might be a tiny bit off (because you are also weighing the contaminant). If your ingredients are food-grade, some contamination is allowed as long as the contaminants are not harmful for consumption.

If you would like to figure out which one may be contaminated, you could repeat the steps with only one ingredient per concentrate, then dilute them in some distilled water at the same ratio, and see which of the final products precipitates. My suspicion would be that either KHCO3, MgSO4 or MgCl2 may be the culprits. If you want to make sure your contaminants did not introduce large errors on your KH and GH, you can buy aquarium titration tests for total alkalinity and total hardness and test out your brew water. You can gain more precision with these tests by using larger samples of water – using twice as much water will require twice as many titration drops, i.e. it will improve your resolution by a factor 2.

Reverse-Osmosis Water and Bacteria

Question: My reverse osmosis water has a total dissolved solids concentration of 2 ppm. Is there any chance that in these 2 ppm I have bacteria? Also, how long do you think I can store it in the fridge?

Answer: It seems like reverse osmosis filters don’t let most bacteria through, but small imperfections can let a small amount of bacteria pass (read more about it here). If you have a bypass valve obviously you’ll get a ton of bacteria directly from your tap water, but if you’re trying to get very low ppm water like you do, the removal of most (not all) bacteria means you can probably keep your water a bit more than 2 days in the fridge. I wouldn’t be surprised if you can keep it for a week in there, but I wouldn’t try to keep it longer without testing. You should smell your water after a week to make sure it doesn’t smell like an old rag. When you boil your water it will kill off all bacteria, but any toxins they left in the water might survive. Not all bacteria produce toxins harmful to humans, but I think it’s good to err on the safe side.

Cannot find Potassium Bicarbonate

Question: Could I replace Potassium Bicarbonate? Because I couldn’t find it easily in Indonesia.

Answer: Yes I would replace it with NaHCO3; you will end up with a tad more Na+, but that probably won’t make a big difference. I suggest you use the Water Crafter and use the version that has no KHCO3 in it. Don’t just replace the weight of KHCO3 with NaHCO3, that would give you the wrong total alkalinity.

Precision of Store-Bought Water Bottle Volumes

Question: You are very precise with everything in the brew water crafting videos. Do you measure the water in a new 4L QUÉBEC-O bottle before you use it? There is always more in it than 4L.

Answer: You are right, they are often over-filled. As I do not have a great scale for 4 kg measurements, I took an empty bottle and filled it with exactly 4L of water by a couple small batches and marked the water height with a black marker. I then took a picture and kept this in my phone as an approximate reference to remove about the same amount of water every time I open a new bottle. This is probably the biggest source of uncertainty in my brew water preparation, as you suspected.

Verifying Brew Water Composition

Question: How do you verify that you crafted your brew water correctly ?

Answer: I use an aquarium titration kit to verify my brew water, but I do this only rarely. You can find GH (general hardness) and KH (total alkalinity) titration kit at a local aquarium store and measure your hardness and alkalinity. Read the instructions manual carefully, it explains how to take the measurement in details.

These kits have a typical precision of 1 german degree (i.e., 17 ppm as CaCO3). This is not great precision, but it should tell you whether you made an obvious mistake. I suspect that we can distinguish about 10 ppm as CaCO3 in the resulting coffee taste with the typical brew water concentrations I recommend; this is just an intuitive number rather than something I have verified so far. You can get a better precision (~9 ppm as CaCO3) by doubling the recommended volume of your brew water sample (typically 5 mL) for the titration test.

Hanna Instruments also manufacture colorimeters that are more accurate (~5-6 ppm as CaCO3 for typical brew water) and convenient (they display a digital number measurement rather than rely on your eye), but they are also more expensive – make sure you get the freshwater version for KH (model HI-775). For general hardness they only sell a more expensive photometer. All these devices (including aquarium titration kits) require chemical reagents, which are dangerous and cannot easily be delivered – this is why you generally won’t find them online and will need to physically buy them at a store.

I will generally only measure my GH and KH when I first do a recipe, or just KH when I noticed something weird, or after about 6 months to check that I didn’t drift. I sometimes use an electric conductivity meter that gives an approximate reading of total dissolved solids (TDS) but those require you to take the measurement always at a fixed temperature (ideally 25 degrees Celsius) – I do not trust any claims of automatic temperature compensations from the manufacturers, in my experience they don’t work. I currently use this one but it’s very finicky and I’d recommend using the HM one instead if you can afford it. Because TDS meters are generally bad and don’t give you a measurement of true TDS (the electric conductivity to TDS conversion they do is based on faulty assumptions for our brew waters), my brew water spreadsheets can’t predict a value that can be tested. Instead, you can use them to quickly check that your water did not drastically change in TDS from one time to the next, or even to distinguish a gallon of distilled water from one of actual brew water (I find this useful as I sometimes mix them up hehe).

Special thanks to Kathy Gagné for providing the header image.

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