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Topic: The endo/exo thing, was Re: +Benefits of a Darker Roast (SC/TO) (27 lines)
1) From: Ken Mary
<Snip>
The heat flow experiment in Dan's reference may not be directly applicable
to coffee roasting. The temperature was raised a very slow 1C per minute,
where a normal roast profile would be very much faster. What the slow ramp
does is remove all (or most) water from the interior of the bean. Also, the
coffee is heated in a sealed calorimeter "bomb", but we roast coffee in an
open vessel at atmospheric pressure.
What I see in my drum roaster with a thermocouple bean probe is sort of an
inverse of figure 5, with a narrow ENDOtherm from about 203 to 210C. The
typical roast profile leaves plenty of water in the bean until first crack
when it is suddenly released. This release of water cools the bean by
evaporation, a physical rather than chemical reaction.
However, the same chemical reactions still do occur in our roasting. This is
important since that is where the flavors originate. Keep the drying and
equilibration stage below 140C where the reactions begin. Let the profile
between 140C and first crack be fairly fast and without wild swings in
temperature. Reduce temperature at the appropriate time for your roaster
near first crack, so there is enough energy to push through the endotherm,
but not so much that you run too quickly into second.
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