TonyTuanx 

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Recently, I've tried to brew AeroPress soup with a modified technique, which produced the thickest, heaviest in the body cups I've ever tasted. I called this technique a "Soak Pass".

The idea is that the most easily extracted compounds in the coffee are low molecular weight compounds, which contribute to acidity and saltiness, even umami taste perceptions. If you discard the first portion of the brew, you can make the brew more balanced with less sourness and salty/umami tastes. This concept is not new, and some people have been practicing this for quite some time in the context of pourovers, competitions and just brewing coffee at home as far as I know.

However, what I was more interested in was the applicability of this concept to low ratio percolation brews, such as AeroPress soup/espresso-strengths, to enhance the body of the brew. In theory, the latter extracted compounds are less soluble, have higher molecular weight and contribute to tactile sensations more.

I've tried to brew it three times so far, and the results were delicious, in my opinion, of course. Here's what I did:

1) As usual, added 18g of finely ground light roast Kenyan coffee (ZP6S at 1.0) to an AeroPress, tamped with the plunger and added paper filter on top of the puck;

2) Added 27g of room temperature and immediately inserted the plunger and pressed to the bottom of number 4 on AeroPress to drain the soaking water. The first portion of the extraction usually weighted around 8-10g, so the grounds absorbed water at a 1:1 ratio at this stage;

3) Removed the plunger and added 36-54g of boiling water, drained the coffee for around 50-60 sec and pushed to the hiss. The amount of boiling water depended on how much coffee I wanted out, and because the puck was almost saturated in the previous step, the output was usually the amount of boiling water added at this step plus/minus 1g.

I was amazed at how balanced the cups turned out with a lot of sweetness and body. These Kenyan beans were very acidic in other recipes, but with the "Soak Pass" the acidity was just right. Of course, the TDS was less at around 5-6.8%, because the sour and salty first portion contained a huge amount of solubles, but if it's that tasty then I'm all for it.

So I've been gathering data on AeroPress Pourover style brews (this recipe: https://youtu.be/njxTlITJ6Ds), and I noticed something really interesting (which I mentioned in the video): the grind size has a significant impact on the resulting extraction yield, when dose and brewing ratio is kept under constant across different beans with different roasts and processes, albeit the water temperature ranged from 60 to 70C. The data is scarce, sure, so I decided to test out the formula from the linear regression ("before" graph), which predicts 28% extraction yield by grinding coffee at 1.0 on ZP6S.

It did not hit 28%! It only reached 23% EY, which is still pretty high, but I was wondering what might be the reason for it. My first thought was to inspect the puck, and surely enough, it had several channels (see if you can find dark spots):

Hello! Here is weekly review of the brews that I made this week; all of them have been added to my Brewing Database, which you can get a lifetime access to if you subscribe to CoffeeTonoia tier or donate 5$ with your email address, so that I can add you to the Google Sheet. Anyways, here are the brews:

1) Brazil Cerrado (natural, medium roast by Energy Coffee) - brewed several times

1.1) 18.0g (ZP6S at 1.0), 27g boiling water soak and 30.7g boiling water

Method: Modified Espresso-Strength Puck Percolation. No tamp! TBT 2 min 40 sec, 35.0 g out

A bit heavier body, not offensive, drinkable, but a little salty and highly astringent; puck looks HORRIBLE, huge dark area, suggesting channeling; pretty common stuff with boiling soak, I should say. Brix 9.2, so 7.8% TDS and 15.2% EY

1.2) 18.2g (ZP6S at 1.0), 36g boiling water soak and 30g boiling water

Method: Modified Espresso-Strength Puck Percolation. No tamp! TBT 2 min 45 sec, 43.3 g out

Used a cotton pad on top of bottom paper filter to see if the channeling could be reduced; the puck still looks terrible with dark region; still a bit heavier body, still a little bit saltiness. Despite this, okayish niceish brew, I think. Less astringency, less bitterness. Brix 8.2, so ~7.0% TDS and 16.6% EY.

1.3) 18.2g (ZP6S at 1.0), 30g room temp soak and 30g boiling water

Method: Standard Espresso-Strength Puck Percolation. No tamp! TBT 2 min 20 sec, 38.1 g out

Watery, very light body; I actually liked this brew, but it's reeally underextracted. Puck is pretty uniform with some dark regions. Brix 7.8, so ~6.6% TDS and 13.9% EY.

1.4) 18.2g (ZP6S at 2.0), 57g boiling water

Method: No Tamp AeroPress soup (high flow). No soak, just add water and press. TBT 45 sec, 39.3 g out

Silty mouthfeel, unpleasant sourness, felt some fermented apples though? Puck with dark spots. Brix 7.6, so ~6.5% TDS and 13.9% EY.

Hello! So I decided to start documenting my brews to collect the data and see if it can be analyzed in bulk in the future. I totally screwed it up though, because the app where I write down my notes doesn't keep track of date of changes (skill issue). Oh well, I will try to do my best to write down the dates from now on, as well taking some pics whenever it's possible! Here are the brews that I've done this week:

1) Decaf Colombia Manzanares (washed, sugar cane decaf, omni roast by rockets.coffee) - brewed twice

1.1) 17g coffee (ZP6S at 3.5), 250g water at 70C

Method: Puck Percolation for AeroPress pourover-style. Puck prep by tamping and sandwiching the puck between bottom and top paper filters, then pour and 2 min drain.

Very nice, sweet and balanced coffee! Posted on YT shorts and repeated it for long-form video. Didn't measure EY%, but a week ago this recipe landed at 19% EY.

The output on average is 225g.

1.2) 18.2g (ZP6S at 0.5), 60g water at 65C

Method: No Tamp AeroPress soup (high flow). Grind, add grounds and level them, add top paper filter, pour, one push for soak to just around number 3 on AeroPress and then push with all my strength. Total brew time (TBT) ~40 sec, 44.9 g out.

Kind of umami, not offensively bitter and not very acidic, just kind of strong and little boring; Brix at 7.7, so around est. 6.5% TDS and 16.1% EY.

2) Uganda Rwenzori (natural, "espresso" (looks medium) roast by QQ Coffee)

18.2g (ZP6S at 1.0), 60g water at 60C

Method: No Tamp AeroPress soup (high flow). TBT ~30 sec, 43.3 g out.

Was okay, had a nice acidity 3/5 with 1/5 bitterness, however it definitely felt underextracted, which was confirmed by Brix 7.9, so 6.7% TDS and ~16% EY. Pretty even extraction overall, but medium to dark roasts always give me trouble in terms of EY!

(EN) An analog Brix refractometer is a useful tool to estimate total
dissolved solids (TDS) in a coffee brew. I use it regularly in my
testings to learn more about how different brewing variables alter the
extraction.

It has been well established that the Brix value correlates linearly
with TDS (https://doi.org/10.1007/s00217-013-1917-x),
and the commonly used conversion formula is as follows: TDS (%) = 0.85 x
Brix. There were also independent studies that replicated this observed
relationship between Brix and TDS (https://doi.org/10.13140/RG.2.2.10679.27040, https://quantitativecafe.com/2022/06/16/calibrating-a-cheap-refractometer/).

I admit, I have yet to read these studies in their entirety. However, one must still
be critical of these formulas, especially when the formula comes from a
correlation. And I still needed to at least calibrate my refractometer,
so I used some instant coffee to see if this relationship holds true.
To my surprise, a linear regression gave me TDS (%) = 0.99 x Brix for
instant coffee, which was very interesting! It is just one experiment,
but I plan to repeat it with different instant coffees with multiple replicates, as well as use sucrose/sugar dilutions as control/reference samples.

Why is this important? Well, the relationship between TDS and refractive index (RI) was established by gravimetry method, i.e. by oven drying coffee samples and weighting the residual solids. After that, the relationship between the weight and the RI measured beforehand is analyzed. But wait, what about RI measurements after oven drying? What if the RI was lower, if the dried samples were to be dissolved in the same amount of water as in the initial sample? Then the TDS that is calculated in commonly used refractometers for coffee is underestimated. Maybe I'm missing something and should do more research, which I intend to do. I will continue my thoughts in the next post about refractometer, as well as dive into some experimental details. For now, here's a messy Excel sheet with results from the aforementioned experiment (at the end of this post).

(RU) Аналоговый рефрактометр по шкале Брикса - это полезный инструмент для оценки количества растворенных частиц (TDS) в кофе. Я пользуюсь им постоянно в моих тестах, чтобы лучше понять, как разные переменные в заваривании меняют экстракцию кофе. Известно, что значение Брикс линейно коррелирует с TDS (https://doi.org/10.1007/s00217-013-1917-x), а формула для перевода значений Брикс на TDS такова: TDS (%) = 0.85 x Брикс. Независимые исследования аналогичным образом установили такую же зависимость между этими параметрами (