Coffee Data Science
The Strange Effects of Quenching in Coffee Roasting
Cooling coffee faster
Initial tests showed some promise to quenching at the end of a roast. This is not an uncommon practice in coffee roasting, and I’ve been exploring how it affects espresso. I did a few more roasts to look at 2 grams and 4 grams of added water during quenching, but the results were mixed.
I added water to 100 grams of roasted coffee using a spray bottle. I measured the weight of the bottle before and after, and I calibrated roughly the number of pumps (~10 per gram) to get to a desired weight. The input green coffee weighted 120 grams, and usually the roasted result was 100 grams.
Metrics of Performance
I used two sets of 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).
Shots
I looked at 4 roasts, and while some shot pairs were much better with quenching, this was not the rule. I had 8 paired shots with 2 grams of water and 16 paired shots with 4 grams of water.
I didn’t see much of a benefit between 2 g vs 4 g.
Each roast had 4 paired shots, and I suspected the quenched shots didn’t age as well because these paired shots happen over a few days. So I looked at the first, second, third, and fourth shot. The first shots were always better. By the time you get to the third and fourth, the shots are more mixed or worse.
Looking at the averages for taste components, the differences did not show much difference between 2 g and 4 g.
On the TDS/EY side, there was not a pattern.
From a statistical level, most of differences were not statistically significant according to a two tailed paired t-test except for Sour in the N=8 2g test. However, that data set is small, so I don’t hold that value in much confidence.
While quenching seemed very interesting, it causes some effect that is not quite desirable in some of the shots. I’m not sure exactly the function, and I may return to this exploration later. This has under-performance vacuum freezing after roasting which was far clearer of an improvement but more difficult of a process.
If you like, follow me on YouTube and Instagram where I post videos of espresso shots on different machines and espresso related stuff. You can also find me on LinkedIn. You can also follow me on Medium and Subscribe.
Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
