Thursday, January 19, 2006

   from AndyS

Inside out with John Gant

Between pours at the Clover demonstration, I chatted with Gimme's roaster John Gant.

He is fascinating and fun to talk to, although this may not be apparent in most of the pictures I have of him. He usually looks very serious, as in this one where he poses with his heirloom Sivetz sample roaster:


(I think you can still buy one of these roasters direct from Sivetz for about $1000. :-) On the other hand, sometimes luck shines upon me and I capture John smiling in a photograph:

Anyway, at the demo I asked John about the statement George Sabados had made in Barista magazine: that the updose technique didn't seem to work with "two dimensional" coffees. Hmm...what's a two-dimensional coffee, you may ask? George says, "In the U.S., coffee is often roasted two-dimensionally, where the outside bean color does not vary greatly from the degree of color in the grind. This narrows the band of resistance to temperature and pressure, and therefore, my method of dosing is not recommended."

Gee, I said to John, I thought the idea WAS to roast more-or-less two dimensionally, at least for espresso. If the inside of the bean is a lot lighter than the outside, it tends to make a sour espresso. John got some roasted beans and a knife, and we cut open some beans. There were different shades of brown inside, because the bean doesn't have a uniform internal structure. Some parts necessarily roast differently than others. But still, the overall impression was that the inside was almost the same color as the outside.

Then I said to John that it seemed to me that the inside would ALWAYS be at least a wee bit lighter than the outside, because the roasting process necessarily heated the bean from the outside in.

Here's where he said something interesting that I hadn't thought of, and it's sort of the whole point of this post: John said that the beans DIDN'T heat solely from the outside in, because of the exothermic reactions that occur late in the roast. These reactions liberate heat and actually produce a heating effect that goes from the inside OUT.

Neat, that had never occurred to me and it alters the way I look at roasting. Those beans become little energy factories, and this exothermy provides heat that can help you roast from the inside out as well as from the outside in. IF you control the process with precision.

I guess this must be obvious to roasting pros, but it was a new concept for me....

12 Comments:

Anonymous JIm said...

I think you may have your endos and exos mixed up...

Isn't heat generated within the bean endothermic?

1/20/2006 04:42:00 AM  
Anonymous AndyS said...

>Isn't heat generated within the bean endothermic?

No. Here's a definition, courtesy of Wikipedia:
"Exothermic Reaction: A chemical reaction that produces heat as a by-product."

BTW, John Gant estimates that 10% of the heat needed to roast the beans comes from internal exothermic reactions. The other 90% has to be applied by the roasting apparatus.

1/20/2006 08:29:00 AM  
Blogger chris said...

yup. This is why you sometimes see beans that have "scorched" looking tips and when you cut them open you see a dark layer in the center of the bean (sometimes called "chimmneying"). It's often the result of overloading your roaster.

1/20/2006 09:58:00 AM  
Blogger trish said...

so....overcharging your roaster will cause tipping? You sure about that?

1/20/2006 01:52:00 PM  
Anonymous Marshall said...

Andy,

Did John tell you the story of how he literally walked away from his law practice in San Francisco one day to become a roaster?

1/22/2006 07:42:00 PM  
Blogger AndyS said...

No, I never heard that. I'll be sure to ask him about it though.

1/22/2006 08:22:00 PM  
Anonymous keith said...

Chris, What is chimneying?

1/24/2006 06:13:00 PM  
Blogger AndyS said...

Keith, you're asking the wrong Chris. If you want to know about chimneying, talk to Kris Kringle. :-P

1/28/2006 02:06:00 PM  
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