HomeRoast Digest


Topic: "The Roasting Concepts" (2 msgs / 71 lines)
1) From: Jeremy DeFranco
     Hello everyone, here is a must-have, gap-filling roasters' companion
that I have just read and now recommend: SCAA THE ROASTING
CONCEPTSIt
gives some very interesting insight, esp. when it comes to proper
roast
temps (401-425 CHAMBER temperature is the "sweet spot" to be in during the
majority of the roast- this is where you get a linear ratio of degradation
of trigonelline to derivation of nicotinic acid, the most favorable Best
Reaction Ratio (BRR)- to achieve the greatest cup) [P.S.- this means I will
be cranking down the GeneCafe to 425! my next roast].  Other great info
includes how to keep fresh roasted beans the freshest (If you can't wait,
the answer is in the freezer, in an odor-sealed canister- the WHY of this
can be found in the book), whether or not to use one-way valve bags (the
answer is absolutely, if you are giving it away to friends- but don't
squeeze it, as you will be literally squeezing out the aroma as well as the
CO2!), a description of the entire roasting process, and much much more!
      Best Wishes and Happy Roasting, Jeremy

2) From: Vicki Smith
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 225-230C, 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 240C.  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 
purchase.
vicki
Jeremy DeFranco wrote:
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