Coffee Data Science
Coffee Roasting: Batch to Batch Consistence
10 roasts back to back
One of the key measures of a good coffee roaster is batch to batch consistency. This is super important for commercial roasting as well as roasting multiple samples in a row for fair comparisons. To test the consistency on the roast, I did ten batches back to back.
At the end of each batch, I would wait for the temperature to dip below the charge temperature and come back up to the charge temperature before adding the next batch of green beans.
Roast Profile
I used Scott Rao’s roast profile on the Roest that uses bean temperature as turning points for inlet temperature. This is my baseline profile.
Data
Only the first roast was off for bean temperature, and the roast took a bit longer.
The Rate of Rise (RoR) was the same for all the roasts with a little noise.
The first crack times had some variations and the maximum number of first cracks. While the first roast had a later first crack time, it had a similar pattern as the others.
We can look at this data slightly differently by look at the Bean Temperature at specific times in the roast. Each roast aside from the first one looks to be within 5 C of each other.
We can look at total number of cracks at a few times, and the number of cracks has more variance.
Post-Roast Metrics
The weight loss was within 1% of each other.
For roast moisture, there was still a bit of variation. Even a 0.1% variation seems like a bit, but it could be worse.
Coffee color had some variation, but this fluctuation is small relative to how much color measurement varies within a single batch.
Coffee density was also pretty close to one another. This gives a bit of a noise envelop when evaluating roast data.
Roast time had a variation driven by the first roast running long, and without that roast, the the difference seems to be within 0.1 minutes or 6 seconds.
These roasts had pretty good consistency between the roast data from the Roest and from the post-roast metrics.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
