Heater Fan Modifications for Coffee Roasting

Fan Trials

Robert McKeon Aloe
3 min readJun 21, 2024

One of the debug modes on the Roest to see how modifying the heater fan would affect the roast. The Roest has a heater fan and an exhaust fan. An increase to the heater fan could cause positive pressure in the roasting chamber. Similarly, a lower heater fan or higher exhaust fan will cause a negative pressure. Before I explored the impact on taste, I wanted to look at a test roast.

For this test, I switched from a standard BT/IT profile to thermal pulsing as thermal pulsing has become my new baseline.

My prior tests showed exhaust fan speed has a large impact on roast speed. Usually, a slower fan speed means a slower roast for 100g roasts. The challenge is that the batch size will also have an impact.

Looking at a few roasts for the heater fan, a higher heater fan speed had a similar effect as a higher exhaust fan speed.

The Rate of Rise (RoR) became more affected as the roast went on. All three had similar patterns with some offset.

All the roasts had similar crack patterns.

Post-Roast Data

The 4000 setting caused the roast to go faster, so while they had the same time post FC, that roast came out darker as can be seen by these metrics.

There is a slightly lower moisture. I’m not sure if the moisture of roasted beans is useful.

In terms of water activity, they all have pretty similar levels.

Color shows a darker roast for the higher heater fan.

Density is also indicative of how dark the 4000 roast is.

These tests show an impact to the roast. I’m unsure if there is explicit value in modifying heater fan vs exhaust fan because both can produce the desired effect of higher air pressure inside the chamber. I did not have a tool to measure the air pressure of the chamber.

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Robert McKeon Aloe

I’m in love with my Wife, my Kids, Espresso, Data Science, tomatoes, cooking, engineering, talking, family, Paris, and Italy, not necessarily in that order.