[Homeroast] Roasting based on crack sounds

Mike Davis mldavis2 at sbcglobal.net
Mon Jun 16 12:49:01 CDT 2014

I start with a disclaimer that I am a relative newcomer to the home 
roasting scene, having started a few years back with an iRoast2 and 
recently upgrading to a Behmor.  My experience with both types of 
roasters has revealed some variables that make roasting more of an art 
than a science.  Here are some observations from past years of roasting 
small batches (1/3 to 1/2 lb.).

The sound of 1C varies with the bean origin.  I suspect the moisture 
content and bean size is also a factor, with (for example) peaberry 
reaching 1C a bit sooner than normal beans.  Interesting that the paper 
was written by the Acoustical Society of America rather than experienced 
professional roasters.

Following a back to back roasting of the Ethiopian Shakiso with the 
Rwanda Karenge, using the same 1# P1 setting with a 1:30 preheat and a 
30 second door crack to extend 1C, the 1C of the Ethiopian was more 
gradual in starting, lasted a bit longer and seemed to transition 
smoothly into the beginning of 2C.  The Rwanda had a sharp 1C onset, 
lasted about 1:30 and ended abruptly.  2C was almost inaudible or at 
least undetectible to my ear aside from a few whimpering little pops.  
Additionally, these origins are often roasted a bit differently with the 
Ethiopians a slight bit lighter. Most of the time, 1C is obvious.  What 
is less obvious with some beans is the transition from 1C to 2C, and /or 
actually hearing 2C begin.  Most of us don't roast through to the end of 
2C, especially with Africans, so the onset is important, not only in 
being able to hear it, but in deciding where it started.  15-30 seconds 
one way or the other makes a huge difference.

So there are some variables to consider which, for those of us who roast 
different batches constantly must learn to recognize and control.  I 
don't think you can write a set of guidelines that will reliably hit the 
sweet spot based on time, on temperature or on sound.  If there are 
guidelines, they are just that - guidelines - a starting point of 
departure in the quest for the perfect roast.

The quest continues, and every little bit helps.  Interesting article.

Mike Davis

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