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% !