To bloom or not to bloom (Part 2)
Updated: Apr 7, 2020
Experimentally measure the effect of coffee bloom on dissolved CO2 in coffee brewed with V60 and Aeropress normal method.
From Part 1 to Part 2 of this research
As this article is the second part of the experiment, if you haven’t read Part 1, please find it HERE. It is essential to read it as in the first part I explain what coffee bloom is, why blooming hypothetically is needed, on what kind of analytical method is my experiment-based and why I used TOC (Total Organic Carbon) as a measuring technique. These are the basics needed to understand the second part of my research.
In this second part, I’m focusing on the same measurement but for coffee samples, prepared on V60 and Aeropress Normal method.
The idea is to see the effect of the coffee blooming procedure on dissolved CO2. In the first measurement, I analysed samples prepared with Aeropress Inverted method which is an immersion method. In the second part, I used V60 as a full pour-over method and Aeropress normal method as a mix of pour-over and immersion. In this way, I will cover most of the differences in all brewing methods and the result could be transferred to other pour-over or immersion techniques.
A series of samples were prepared by the following procedure.
For the V60:
1. 15g coffee, ground for V60;
2. 94°C Water temperature;
3. A total of 250ml of water was used for all samples added on 3 equal parts;
4. Total brewing time around 2:50min;
A total of 6 samples were prepared – 3 with a blooming time of 30sec with 40ml of water. The rest of the water (210ml) was added on 3 equal parts. The total brewing time varied from 2:50 – 2:54 min. When no blooming was used for the other 3 samples the entire water was added on 3 equal parts. Preparing the V60 coffee this way the total brew time varied from 2:52 – 2:56 min. Immediately you may notice that the total brewing time for samples with or without blooming stays the same provided that all other parameters are constant.
Here I must thank my friends from Snack! Specialty Coffee for the help, hospitality, and expertise in V60 preparation. They used Mahlkönig EK43 for a grinder, Hario V60 filters, and Acaia Pearl scale.
For the Aeropress Normal method:
1. 15g coffee, ground for Aeropress;
2. 85°C Water temperature;
3. A total of 200ml of water was used for all samples;
4. Attach the plunger at 1:00min;
5. 30 sec for plunging;
6. Total brewing time of 2:00 min for all samples;
7. 6 gentle stirs at 0:45min mark
6 samples were prepared – 3 with blooming time of 30sec with 50ml of water and 3 without blooming, where the entire water was added at once. All other parameters were kept constant.
All samples were enclosed in centrifuge tubes, firmly closed and stored at the fridge until analysis. Lowering the temperature will draw the CO2 equilibrium to the dissolved CO2 and carbonic acid formation. Samples are kept in the fridge until analysis. For the TOC analysis 1ml from each sample was transferred to 50ml centrifuge tubes and it was diluted with 49ml of ultrapure water. Samples were gently stirred 2-3 times and were loaded on the TOC instrument. An injection volume of 300 microliters was injected for TOC analysis based on the measurement of TC and TIC. The instrument measured 3 times each sample for better statistical results.
I must mention again, that for this experiment no calibration curve was required because it is a comparison analysis, not quantitative analysis. Together with all coffee samples, tap water, filtered water, and ultra-pure water was analyzed, so the results could be evaluated more correctly. No quantitative analysis is needed so for the results, peak area was evaluated as an absolute value of Area Units (AU).
Some of the people who read Part 1 of this experiment commented that the results were predictable as blooming shouldn’t have any effect on dissolved CO2 in the immersion method.
Most of them suggested that blooming should have a bigger influence on pour-over technique like V60.
In any case, there are plenty of YouTube videos showing and explaining that blooming is mandatory for both methods. I have to say that there is a difference between suggesting and experimentally prove something. My project is to measure and prove if blooming has any effect on dissolved CO2 in all brewing methods. I’m not led by suggestions and opinions and that is why I had to research both methods.
First, I measured again Ultra-Pure Water and Tap Water. Aeropress samples were prepared in Sofia with tap water rated as Very Soft (0-4 dH), and V60 samples were prepared in another city – Plovdiv, where the water is rated as Middle Hard to Pretty Hard with value on 8-18 dH (German degrees). Results measured by the TOC analyzer confirms the expected value of the water hardness and IC (Inorganic Carbon) values for tap water in Plovdiv is 4-5 times higher than the water from Sofia (Table 1).
And now the interesting stuff…
Even thou the Aeropress Normal method (ANM) is a mixture of immersion and pour-over technique, the results for all samples are absolutely the same as the one achieved from the previous experiment with Aeropress Inverted method. The average values for all 3 repetitions with and without blooming are 628AU and 687AU respectively (Table 2). The difference in IC is only around 60AU and like in Part 1 of this research this value is so small that it is negligible. Keep in mind that the difference between water from Sofia and Plovdiv is around 700AU, more than 10 times the difference between samples with bloom time and without.
These results proved that blooming in Aeropress both methods does not affect CO2 removal. Hence the dissolved CO2 stays constant no matter how the coffee is prepared if all other parameters are constant. No matter how you prepare your coffee with Aeropress if you stir the coffee even a little bit during the extraction, Inorganic carbon compounds will stay at the same concentration.
Blooming doesn’t play a role in CO2 removal at all.
Let’s investigate the V60 technique. Surprisingly keeping all other parameters constant, the concentration of IC for samples with bloom and without blooms stays the same. Unlike Aeropress methods, in V60 the difference between samples is even smaller and more of a statistical or instrumental error than a rule or trend. The average value for samples with blooming time is 322AU compared with 314AU for samples without. This difference in 8AU is even more negligible (Table 3).
Thus, it turned out that blooming is even more meaningless in V60 compared with Aeropress when it comes to the effect of CO2 removal. This was not what I and most of the readers from the Part 1 article expected. Considering that samples for V60 were prepared with much harder water with initial IC value of 895AU showed that the most important factor is the water temperature. Boiling the water leads to drastically decreased IC value that stays constant no matter how the coffee is prepared (Graph 1).
Comparing the difference between the absolute value for IC in V60 and Aeropress it is clear that V60 removes more CO2 from the coffee.
The difference is not big, and it varies around 350AU, still this is significant. There could be several reasons explaining the measured data. Firstly, V60 is much more open to the surrounding air and the coffee distribution area is bigger. In contrast, the opening of the Aeropress is much narrower compared with V60. This could lead to greater CO2 loss during preparation on V60 as the coffee grounds are more exposed to air and CO2 could be degassed easy and at a higher rate. The second reason is that for V60 we used slightly higher water temperature - 94°C instead of 85°C. Dissolved CO2 in water decreases with increasing temperature. Nevertheless, I don’t think that this effect is worth investigating more than this.
This research goal is to measure the effect of blooming on dissolved CO2 and CO2 removal. And both parts from this research proved that blooming is a nice-looking procedure, but meaningless in a matter of the above-mentioned effect. Blooming doesn't affect the concentration of carbonic acid in the coffee. This also means that the absence of a blooming procedure can't contribute to the sour and acidic taste or at least the contribution related to the same carbonic acid. I’m not saying, “Do not bloom your coffee”. Bloom it, if you want to observe or show the others the beauty of bloomed coffee. Because if someone thinks that coffee with bloom tastes better, I’m OK with that. Taste is subjective and both parts of this research are not focused on taste.
Just don’t say that blooming removes CO2. Brewing coffee removes CO2!
Maybe blooming has an impact on coffee extraction and coffee agitation. Maybe? Who knows?
To be honest, I already know. TOC analyzer is also providing me with results for Total Organic Carbon. TOC represents all organic compounds that are giving the taste, aroma, body, acidity, sweetness and practically everything that is extracted from the coffee. The measurement is much more precise, accurate and exhaustive compared to a simple TDS (total dissolved solids) meter, that could never measure undissolved matter and oils, and could never distinguish inorganic from organic compounds. The difference in TOC could show the difference in extraction.
Measuring the effect of blooming on TOC will give the answer if blooming has any effect at all.
This, however, is a story for another time.
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