Coffee Data Science
Thermal Pulsing in Coffee Roasting: A Deeper Look
More experiments to better understand pulsing
Previously, I found thermal pulsing in coffee roasting provided an improvement in taste. I wanted to better understand how heat moves through coffee, so I used a test coffee and modified the pulse frequency and duration.
Thermal Pulsing
Thermal Pulsing uses a BT/IT profile design on the Roest (a sample coffee roaster) which modified the Inlet Temperature (IT) by the Bean Temperature (BT). This is an example of thermal pulsing:
Number of Pulses
I looked at 2, 4, and 8 pulses. There wasn’t much difference at the beginning of the roast during the drying phase, but later, there were larger differences.
The Rate of Rise (RoR) stayed within the same band, but obviously there were more fluctuations with more pulses.
The number of audible cracks also varied.
Low Dips in Pulsing
I looked at the same profiles, but I caused the temperature swings to dip a lot lower. That’s where things got interesting.
The RoR would stall and get stuck at a certain point. Some times, I would have to turn up the exhaust fan to get the bean temperature over a hump in the profile.
The cracks were different too, but really, the learning was the RoR crash.
So I look a snippet of data where the RoR crashes. In this example, the inlet temperature is around 200C and the bean temperature is around 160C, so it appears at ~40C difference in inlet temperature and bean temperature, the bean temperature can not absorb anymore heat.
This is an interesting finding because knowing the heat drop off for a bean could help to design a profile that still causes the beans to absorb heat without an RoR crash.
Another way to look at the inlet temperature is Inlet minus Bean vs Bean Temperature. The difference bounces around until settling on 40C.
Fan Pulsing
I look a look too at pulsing the fan while doing thermal pulsing.
I ended up with a pretty similar profile as regular pulsing especially in the first two pulses.
Except the profile developed a little earlier. I need to look at fan pulsing more closely and more strategically.
Post-Roast Metrics
In terms of weight loss, the low profiles had higher weight loss in part because they went on for so long.
This doesn’t seem to affect moisture as much, but it is quite possible the moisture meter has trouble at a lower range. Thermal pulsing gave a higher moisture, but with fan pulsing, the moisture went back to the baseline.
The pulses with low drops got a lot darker in part because they roasted for much longer.
Density followed a similar trend.
All of these coffees were only to test these metrics with the aim to use this information to make coffees to taste.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
