I wanted to know what was happening in the Hottop (ET and BT) during the roast, so I installed thermocouples. The main reason for installing thermocouples is that the location of the built-in thermocouple in the HotTop becomes less accurate as you roast smaller quantities of beans. At the start of the roast, it shows the ET, and at the end of the roast it shows the BT. If you roast at least 250g, then the bean mass expands sufficiently to cover the thermocouple. The result is that it shows the actual BT when you get to first crack. But this becomes less likely to occur as you roast smaller quantities.
Conventional wisdom says that smaller roasts get to first crack sooner, which often produces better tasting coffee. I determined my minimum desirable roast size (based on consumption) as 215g for most coffees. So I could not rely on the built-in HotTop thermocouple to give accurate readings.
I waited about three months, in order to learn how to roast on the unmodified HotTop. Now I'm taking it to the next level with Jim Galt's TC4C + HTC board. This will allow me to automatically duplicate prior adjustments to the fan and power, and more easily reproduce a profile for a given bean.
