Coffee Data Science
Extract Cooling for Espresso
Applying modern techniques to hack flavor
Espresso is generally brewed hot, but one of the downsides is that aroma continues to be lost to evaporation. Generally, there is a notion one should drink espresso almost immediately after brewing. The trouble is that espresso is hot, and my experience is that letting a shot cool to below 50C causes a large improvement in flavor. The downside is that if a shot sits for too long, oxidation ruins flavor. What if we cool the shot rapidly after being brewed? We could have the best of both worlds by doing what Hugh Kelly called Extract Cooling
History
I was inspired by the Paragon dripper by Nucleus tools, introduced this year (2022). However, for espresso, this idea was used in competition the prior year. In 2021, at the World Barista Championship (WBC), Hugh Kelly made espresso using some cooling stones to cool the first half of an espresso shot.
However, 2021 was not the first time such a technique was used at WBC. Berg Wu from Taiwan competed in the 2016 WBC using cold portafilters (spouted, not bottomless), with the intent of cooling the first part of the shot, and he won.
But wait! This is not the first time someone has sought to cool coffee quickly. The origin story goes back at least to 2011 when Coffee Joulies came on the market. Their aim was to cool coffee to a drinkable temperature and then maintain that temperature using an encapsulated material which a boiling point near 70C. This means that the material would change from solid to liquid sucking up a lot of heat. Then it would re-solidify maintaining the temperature for longer. The company doesn’t appear to be in business any longer.
Another company called Joeveo started in 2013 with a similar technology in a coffee mug with an aim for 60C. The cup is quite large for espresso.
Both of these technologies didn’t hone in on the idea that aroma was lost, which is the learnings of Sasa and company, but the seeds of this idea had formed previously for other reasons.
I don’t brew pourover, but I thought I could make a hack to test the technique. This was interesting to me because the academic results were not out yet.
So I used a massage rock made from basalt, and I put it in the freezer.
The first few tests were so successful, I didn’t want to do the usual paired shots. However, I did it for science.
Equipment/Technique
Espresso Machine: Decent Espresso Machine
Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)
Shot Preparation: Staccato Tamped
Pre-infusion: Long, ~25 seconds
Infusion: Pressure Pulsing
Filter Basket: 20g VST
Other Equipment: Atago TDS Meter, Acaia Pyxis Scale
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).
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.
Data
I sampled 8 coffees over 20 paired samples. I found the cooled shots tasted better. They read a slightly higher TDS/EY, but that could have been due to the sample being cooler.
The average taste score increased across the board. A 1 point increase could be more noisy of an indicator especially for a small dataset, but most had a 2 point average difference.
Overall, the impact of cooling the sample was statistically significant for everything but EY and IR.
While the cooling experiment was more curiosity than searching for something new, I found a part of my espresso routine has forever change. I continue use a cooling rock as I have found extract cooling is a major methodical improvement anyone could apply. It doesn’t have to cost so much money either, and the results are immediate.
The bigger question to me is understanding what’s going on during brewing and cooling that causes such an effect to be so noticeable.
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