I have to admit it, I'm sorta lost when trying to understand how
roasting chamber temperature translated into bean temperature, so this
kind of information is helpful to me.
I had been looking at information from Davids (as summarized by
coffeeresearch.org) but I was not really sure where exactly the
measurement was being taken.
Found:http://www.coffeeresearch.org/coffee/roasting.htm The second step, often called the first crack, occurs at
approximately 205 °C (400 °F) in which the bean doubles in size, becomes
a light brown color, and experiences a weight loss of approximately 5 %.
The corresponding Agtron number for this color is between 95-90
(Davids, Roasting, 68).
In the next step the temperature rises from 205 °C to approximately
220 °C, the color changes from light brown to medium brown (Agtron #
60-50), and a weight loss of approximately 13% occurs (Davids, Roasting,
68). The resulting chemical process is called pyrolysis and is
characterized by a change in the chemical composition of the bean as
well as a release of CO2.
The second step is followed by a short endothermic period, which is
followed by another exothermic (beans release heat) step called the
second crack. This second pyrolysis occurs between 225-230°C, and the
roast color is defined as medium-dark brown (Agtron #50-45) (Davids,
Roasting, 68). The second pop is much quicker sounding and the beans
take on an oily sheen. Roasting well into the second pop or darker is
not favorable since volatile aromatic compounds are stripped off and
oils on the outside of the bean are more easily oxidized.
Unfortunately, in America the trend is to roast to a dark black, with a
bright-shiny surface, and a final temperature of 240°C. This type of
roast is often preferred since it masks poor blending, dirty machines,
and stale coffee.
Thanks, Jeremy. It looks like this book may be my next non-bean coffee
Jeremy DeFranco wrote: