Coffee Data Science
Yeast Green Coffee Processing: Additional Experiments with Water and Chocolate
Horsing around with yeast
Previously, I did experiments showing the effect on green coffee using yeast. Using yeast processing on coffee fruit has been done as well as on green beans, but there isn’t much information publicly available on green bean fermentation. Generally, yeast processing reduces acidity and bitterness which greatly impacts the sweetness of the bean.
While experimenting with yeast, I did a two extra experiments: water and cocoa powder.
In the water experiment, I was curious if hydrating the beans and then dehydrating them alone was part of why yeast coffee was better. Ultimately, that turned out not to be the case, but I’m glad I went through the experiment as it helped separate a variable.
With cocoa powder, I randomly thought it might be interesting to see how yeast and cocoa powder could influence the coffee flavor during fermentation. I was wishing to create a chocolate coffee, but cocoa powder didn’t seem to have an effect on the yeast.
Equipment/Technique
Espresso Machine: Decent Espresso
Coffee Grinder: Niche Zero
Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)
Shot Preparation: Staccato Tamped and Staccato
Pre-infusion: Long, ~25 seconds
Infusion: Pressure Pulsing
Filter Basket: 20g VST
Other Equipment: Atago TDS Meter, Acaia Pyxis Scale, Kruve Sifter
Metrics of Performance
I use two metrics for evaluating the differences between techniques: Final Score and Coffee Extraction.
Final score is the average of a scorecard of 7 metrics (Sharp, Rich, Syrup, Sweet, Sour, Bitter, and Aftertaste). These scores were subjective, of course, but they were calibrated to my tastes and helped me improve my shots. There is some variation in the scores. My aim was to be consistent for each metric, but some times the granularity was difficult.
Total Dissolved Solids (TDS) is measured using a refractometer, and this number combined with the output weight of the shot and the input weight of the coffee is used to determine the percentage of coffee extracted into the cup, called Extraction Yield (EY).
Intensity Radius (IR) is defined as the radius from the origin on a control chart for TDS vs EY, so IR = sqrt( TDS² + EY²). This metric helps normalize shot performance across output yield or brew ratio.
Water Experiment
I setup the same beans and went through same process, but I left out yeast for one of them.
They stayed in the jars for 24 hours, and the beans soaked up all the water. However, the water processed ones had a liquid coming out. I tested it with a TDS meter, and I even tasted it. It was very astringent and not good. I was unsure if the yeast was consuming that extract because of the sugar content, but I didn’t wash it off when I rinsed and dried the beans. I was also concerned it was decaffeinating the beans, but I don’t have any evidence either way.
The water processed beans roasted very differently. I should have let them go longer, and they were much denser suggesting they had not been developed as much in the roast. This made a taste comparison difficult.
In part due to the roast, the yeast was far better than the water processed beans. I quickly ended the experiment when it was clear that there was never going to be an overlap in taste score distribution. Most of the shots with the water processed beans were difficult to drink straight.
Adding Cocoa to Yeast and Green Beans
I saw the cocoa bag and said “maybe”, so I gave it a go. It made for fun photos.
Both of these looked similar after rinsing.
They both roasted very similarly, which led me to think the taste results weren’t going to show anything significant.
In terms of taste (Final Score), they were about the same. In terms of TDS/EY/IR, the cocoa beans faired slightly better, but overall, it was an experiment I ended shortly after because there was not a good taste gain in sight.
Even though both of these experiments failed to find something new, I still like writing about them because my failures make me who I am today. Research is about banging your head on the wall 100 times for that one brilliant idea.
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