It all depends on your thermometer calibration, probe location, roaster
type, bean moisture, ramp approaching first, and etc. My range for start of
first is 393 to 415 F using a standard profile in my drum roaster with bean
thermocouple. Kenyans seem to start at the lowest temperature, most other
beans at 400, aged or monsooned at the highest.
Faster ramps delay the start of first to higher temperatures. But this is
only because the probe reads the bean surface which is the highest
temperature. The crack is a function of the bean internal temperature which
cannot be measured.
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