Coffee Data Science
Varying Starting Drum Temperature in Coffee Roasting
Let’s see what the difference makes
My current profile on the Roest has a starting charge temperature of 191 C for air inlet temperature. However, this does not mean the drum is warm enough when I start roasting. I typically see a lower drum temperature for the first roast in a series of roasts, so I wanted to check how much drum temperature impacted the end result.
For all of these roasts, the inlet temperature was at the desired charge temperature of 191 C, and I aimed to end them with the same development time.
Post-Roast Metrics
I was able to get the roasts to come out with very similar metrics. There was a slight trend for density, but I don’t know if that is really meaningful.
The 124 C drum temperature had an oddly high moisture content. The coffee color is close, but I wish I would have gotten the 169 C color closer to the other two.
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).
Shot Data
I pulled four shot pairs for the roasts, and this data might give some insight on the topic without being conclusive.
A colder (57 C) was never better than the higher temperatures. The 124 C and 169 C are pretty close.
Resorting the data didn’t give much insight. The shot pairs had other parameters involved which caused some fluxuations.
EY was not affected throughout all the shots.
A cold drum is not really feasible in back to back roasts. Around 130 C is where the drum settles after a cold start, and 169 C is closer to starting a roast soon after the last one. If I continued to experiment, I would shift to 100 C, 150 C, and 180 C. However, I didn’t see something drastic in the taste results that indicate I should do anything different aside from continuing to make sure the drum is warmed up sufficiently.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
