To bloom or not to bloom (Part 3)
Measure the effect of blooming on coffee extraction
Continuation from Part 1 and 2
At the beginning I need to say, if you are not familiar with Part 1 and Part 2 of this research, you have to check them HERE and HERE. It is crucial to read them both since I’m explaining all the theory and chemistry behind this experiment, but also providing you with the general idea of blooming and its effect on coffee.
When I started this project, it was planned to be a simple experiment that could be summarized in a single article. Yet, with each subsequent step during the research and sample measurement, more and more questions were rising. So I finally realized that there is so much more to analyze and too much information that a single article can bear.
When I promoted this article, I was thinking to evaluate the TOC (Total Organic Carbon) of each coffee only, but later on, I decided that TC (Total Carbon) will be more appropriate to be measured. This is because TOC is calculated as a difference between TC and IC (Inorganic Carbon), and we already saw that IC is constant no matter how the coffee is prepared. Using TC values to measure blooming will give equal results as to use TOC values, but since TC measure is easier and faster, I preferred the TC.
You probably have learned from Part 1 of this research, that TC is the sum of organically and inorganically bound carbon present in water, including elemental carbon. It is strongly related to TDS (Total dissolved solids) because almost every compound extracted from the coffee contains carbon. However there is a little difference – TOC/TC measurement is taking into account the undissolved matter that is sometimes ending in your drink, and extracted oils not soluble in water, most commonly floating on the surface of the coffee. TOC instrument is like a precise TDS meter with pumped extra functions. The coffee sample is injected in the catalytic combustion chamber filled with platinum catalyzer at temperatures of 680 °C. This leads to the conversion of all organic and inorganic molecules (and elemental Carbon) to CO2 which then is detected by a non-dispersive infrared detector.
The Goal of Part 3
The main goal of this experiment is to measure the blooming effect on coffee extraction using different methods – immersion, pour-over, and mixed-method. For this purpose, I used Aeropress Inverted, V60, and Aeropress Normal methods respectively. Measuring and comparing the TC concentration in the coffee prepared with and without the blooming step will show us if blooming affects coffee extraction at all. It will prove or disprove the second hypothesis that is related to blooming – that releasing of the gases is mandatory as it will block the contact of water with the coffee and will lead to under extraction. Just to mention, that in Part 1 and 2 of this project I already disproved the other hypothesis about CO2 removal and CO2 effect on coffee taste. In short - blooming doesn’t affect the concentration of CO2 ending in your cup of coffee.
The sample preparation is the same as the one used in Part 1 and Part 2 of this research. The only difference in the TOC analysis this time was that the instrument was switched to measure TC value and not IC. Results will be evaluated based on the measured TC absolute area listed as Area Units (AU). Since this is a comparison analysis no calibration curve is needed. All variables during brewing were kept constant with the only difference – the blooming step.
In the results table below I used abbreviation related to the different extraction methods used as follows– AIM (Aeropress Inverted Method), ANM (Aeropress Normal Method), and V60… for V60.
I’ll start will the commonly used Aeropress Inverted Method. The Inverted Aeropress is a representation of the immersion method where the coffee grounds are in constant contact with the water. There are some controversies about the blooming step in this method as many are not using it and claiming that blooming is not effective. However, there are many still using it and posting recipes, articles, and YouTube videos. The general hypothesis is that CO2 is restricting the water-coffee contact and without using a proper procedure for CO2 removal (e.g. blooming step), the extraction will be troubled.
What do you think the TC measurement showed?
You can see from Table 1 that there is little to no difference between extractions with and without blooming when preparing coffee with AIM. There is only a 0.2% average difference in the TC concentration after doing 4 repetitions for each sample. We need to take into account that 140000 AU is equivalent to about 1.4% TDS, which gives us a difference roughly about 0.0028% in TDS.
Graph 1 shows the average value of TC for samples prepared with and without blooming time.
Another unsuspected tendency is emerging from the data. On average the extraction of coffee prepared without blooming is much more consistent. It could be suggested that adding the entire quantity of water is preventing dry spots in the coffee bed. The coffee beans are soaked more evenly, and the extraction is starting roughly at the same time. Another explanation is water temperature. Adding the whole amount of water into the brewing chamber is preventing significant temperature differences among the coffee particles. Adding only 50ml at the beginning of the blooming step could create places where the coffee temperature is higher and places where it is lower. Regarding the immersion method, it looks like the stirring is much more important for even extraction. The repetitive extractions are shown in Graph 2:
The standard deviation of samples prepared with blooming is around 2.5 times higher than the standard deviation of the ones without blooming. This conclusion was quite unexpected for the immersion method like the AIM. Converting the results in %TDS it appeared that the deviation in extraction with blooming time is more significant and could reach to approx. 0.02% TDS. This value is measurable with a standard TDS refractometer.
Let’s now look at the results for the Aeropress Normal Method showed in Table 2.
It looks like using Aeropress Normal Method the blooming step is increasing the extraction efficiency. The values show that there is a significant difference in the average extraction when comparing the method with and without blooming...
You can continue reading the entire article on my Patreon page HERE. There you can find the results for the Aeropress Normal Method and V60, as well as some conclusions based on the observed data.