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endothermic reversal point
JETROASTER
I came across this little term and thought someone might help me to understand.....Marshall?
-Scott
Edited by ginny on 11/12/2013 11:46 PM
 
Dan
I've never heard that three-word term before. During coffee roasting the process begins as endothermic (taking in heat), but after second crack it becomes exothermic (giving off heat).

There was a time in the home roasting community that many people believed roasting was endothermic throughout the roast, but this has been proven false.
 
http://www.intactamerica.org
allenb
I've heard many different takes on this but I thought it was endothermic up to 1C, exothermic during 1C and a little after 1C got rolling it reversed and again became endothermic?

I'd love to hear some concrete info on this once and for all.
Edited by allenb on 08/13/2010 2:04 AM
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
seedlings
"Until the start of the first crack, the heat inside the beans is endothermic; the beans are absorbing the supplied heat. Right before the start of the first crack, the heat inside the beans becomes exothermic and the beans start generating heat. At this point the operator has to reduce energy supply in order to gain control of the roast process. After about two minutes of controlling the roast with low energy supply (less BTU), the operator can again increase heat (endothermic heat; the beans are again absorbing heat) to prepare for the finish of the roast."

http://www.bootco...iling.html

Right on, Allen.

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
 
JETROASTER
Does that suggest an exothermic reversal as well? -Scott
 
seedlings
freshbeans wrote:
Does that suggest an exothermic reversal as well? -Scott


The diagram shows exothermic during first and second crack, this would mean that after first crack it reverses from exothermic to endothermic, so yes, there are endothermic reversal points and exothermic reversal points. My guess is the endothermic reversal point would be at the first signs of first (or second) crack. The exothermic reversal point would be at the end of first crack (and again, dare I say, at the end of second crack).

www.bootcoffee.com/scurve_v3a.jpg

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
 
allenb
Very interesting!

Willem Boot is concrete enough for me.ThumbsUp
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
John Despres
If there's a reversal, I'd guess your temperature is dropping... Maybe that's the cooling phase.
John
Edited by John Despres on 08/13/2010 3:13 PM
Respect the bean.
John Despres
Fresh Roast 8, Gene Cafe, JYTT 1k, Quest M3, Mazzer Mini, Technivorm, various size presses and many more brewers.
 
www.sceneitallproductions.com
endlesscycles
Until the beans are on fire, they are taking heat, not giving it off. Second crack may qualify as on fire to some extent. First crack is simply giving off moisture, which in a drum with the related increased rate of convection may appear to be exothermic, but isn't.
-Marshall Hance
Asheville, NC
 
seedlings
Without personal knowledge, I defer to Boot.

CHAD
Edited by seedlings on 08/13/2010 4:07 PM
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
 
JETROASTER
I've always been under the impression that at the point of pyrolysis, the beans would 'produce' heat thru some alchemy that
I don't understand.
When I bought the Sivetz heat gun roaster, it came with a strange 20 page Manifesto written by M Sivetz and edited by someone worse than me.
I just took that bit of info for granted. The gauges seemed to support it.
I can not say I've seen the first reversal on the gauges. The second one I see everyday.
At the end of a darker roast, gas gets turned way down and bean temp continues to climb.
What's the skinny on this matter?? -Scott

 
seedlings
freshbeans wrote:
What's the skinny on this matter?? -Scott



Exothermic internal chemical reactions producing heat.

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
 
allenb
Scott,

When the 1C exothermic reaction occurs, the beans are truly generating heat internally but due to vapor release there isn't a rate of rise increase for some of us. In one of my roasters which is radiant only (due to my convection element burning out), the RoR comes to zero just prior to and during the first seconds of 1C and I have to increase power to compensate.

My guess is that at 2C the exothermic action does not produce as much vapor which causes a RoR increase requiring a power reduction.

The reversal for 1C has a totally different affect on RoR and power input needs versus 2C reversal.

That's my theory.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
JETROASTER
That theory makes some sense. On a different thread I had noted a RoR plateau (at a lower temp range) before 1C. I assumed it was evaporational cooling. Considering the gauge may not be trustworthy, that seems to fit.
So, it sounds like the exothermic is masked by the moisture loss at 1C , not so much at 2C.
Sounds like all this looks different on drum vs air-roasters .
I'm roasting Monday.....we shall see

As always ,Thanks -Scott
 
Dan
What I know about this, and that is very little, is that the roasting reaction is endothermic when the inside of the bean is cooler than the outside. Exothermic is when the interior of the bean is hotter than the exterior.

I'm not sure how Boot determined those points on the curve were exothermic because he doesn't show that he measured the interior temperature of the beans, only the bean mass, which is the exterior of the beans.
 
http://www.intactamerica.org
JETROASTER
So if the bean is hotter inside than outside, is this accumulated heat from roasting, or is it heat that is being chemically created?
-Scott
 
Dan
Chemically created, that's why it is called an endothermic (chemical) reaction. Essentially, the bean is beginning to combust. Not enough that it can sustain the reaction yet, but given a little time it will begin to burn.

 
http://www.intactamerica.org
seedlings
Has to be heat generated from chemical reactions, Scott.

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
 
Ringo
Just a guess on my part but 1st crack is when the steam breaks open the bean, I always guessed this released steam is the heat.
All you need in life is ignorance and confidence, and then success is sure. Mark Twain
 
Dan
Yes, steam is releasing heat since it is hotter than the environment, and it does tend to remove heat from the bean, making it an exothermic process, but it is not an exothermic CHEMICAL REACTION since the water/steam started and ended as H2O. That is there was no chemical reaction, just simple heating and cooling.
 
http://www.intactamerica.org
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