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temperature versus color - the art of roasting?
yamhill
I just got a new batch of green beans - some decaf and some regular. Both are espresso blends from Sweet Maria's. I typically roast based on time and temperature. When I roasted a batch of each of the new beans with the same profile, I was surprised at the difference in color.

Here's some more detail on my roast method. I use a popcorn roaster with a variac on the heating coil and a dimmer control on the fan. I measure temperature with a thermocouple in the beans. I have developed a practice of judging the roast based on the bean temperature. I'm generally using a 4,4,4 to 5,5,5 profile (time to 300, time to 400, time to final temp). My batch size is 95g. The last two batches had a very similar roast profile, and they look very different. The 450 final temperature looks much lighter on the caffeine batch.

I'm looking for advice on judging the roast. Which is dominant, color or temperature? Should I judge roast on color or bean temperature? Temperature is less subjective and easier for me. Is this simply me stepping into the art of roasting versus the science?

John
JETROASTER
I go mostly by temp.
I find measuring temp at the exhaust port gives me a better result than measuring the bean mass. The reasons for that probably deserve a seperate thread.
Measuring temp above the bean mass has given me more consistant results(from one bean to the next) than measuring in the bean mass.
Decaf are likely going to look odd anyway.

I agree that temp is less subjective, and more reliable. It may just be a matter of finding the best location to get your reading. Good Luck. -Scott
Edited by JETROASTER on 06/03/2011 2:57 PM
seedlings
Yep. Decaf usually looks like City+ before it goes into the roaster, and you're better off going by temperature.. even the aromas are different during the roast. Decaf will usually hit second crack at a lower temperature when I roast.

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
yamhill
I'm not sure that I understand the value of measuring the temperature of the exhaust versus the bean temperature. Wouldn't the bean temperature be the most direct and accurate way to judge the roast? I would love to understand the factors involved here.

Color isn't the only difference that I observed between the decaf and regular. The intensity of the smell was also very different - the decaf being more intense. This is the opposite of my previous experience.

John
endlesscycles
I've noticed the exhaust temp is pretty much the bean temp, and I can definitely see reasons to use it instead (faster response). Rate of temp during the final thirty seconds is also valuable to final degree as not only instrument error but roast depth are affected. Total time spent over 426F is also important.
-Marshall Hance
Asheville, NC
JETROASTER

Quote

yamhill wrote:
Wouldn't the bean temperature be the most direct and accurate way to judge the roast? I would love to understand the factors involved here.

The intensity of the smell was also very different - the decaf being more intense. This is the opposite of my previous experience.

John


On the measuring point; It seemed that in the bean mass, I was closer to the heat source, creating an illusion of higher bean temp. Too much of an enviromental reading.
My only theory so far is that the exhaust reading is indicating energy that the beans are rejecting.
What I know for sure is that the results are consistent, and I've tried to proof myself wrong. I've forced loads, I tried dragging them out. Winter, summer, whatever.
The only reason I monitor the bean mass anymore is to see if I'm forcing the load.
I'm hoping some folks smarter than me might chime in on the exhaust reading... it's got me a bit stumped.

On the decaf. Hmmmm. Perhaps the cell walls are more damaged to begin with?
Great questions. My hunch is that some good answers will come your way.
-Scott
yamhill
I can see the basis for some experimenting in my next roasting session. I'll move the temperature probe above the beans to see what happens.

I've observed that decaf typically takes less energy - a lower variac setting - to achieve a given temperature.

The input here is very helpful.

John
DavidG
Quick clarifying point here... Scott is referencing his gas fired roaster, and I think Marshall roasts on a commerical drum with gas (forgive me, fellas, if my memory is wrong). John, if you are on a mod'd popper, then the discussions of exit air temp and bean temp need to be put into context. Also, your load is 95 grams -- essentially, exit temp (i.e. air above the whirling beans) may varying some from the temp taken within the 95grams of beans, but not by a whole lot, I would think.

At the moment, my poppers have the therocouple probe on an angle through the lofted bean mass to a point in the center of circular chamber at a height 1.5 inches from the floor. I measure the air/bean temp. First crack comes around 385 to 395F for me, with this setup.

And, +1 on all the comments about decaf. My experience is that they roasts fast, color is always off, smells are tricky and sometimes 1C and 2C can run right together.

Cheers,
DavidG
europiccola | yama + coryrod | chemex | AP | clever
wbp1 | wepp1 | bm/hg | co hybrid (still coming soon...)
allenb
I agree you should try and read exhaust if finding a place in the bean mass without roasting convection air influence is not possible.

My bean probe (fluidbed roaster) is also sensing exhaust instead of bean mass and I, as many here at HRO, see 1C occur between 395-400+.

I agree with Scott that it doesn't make sense why the combination of roasting convection air and beans would yield a useful bean temp but I've gotten the same temps when sensing beans only in my drum roaster. Somehow the exhaust temperature is pretty darn close to the actual bean mass.

Ditto on the decaf. The few times I've roasted decaf I did find I had to treat it as I do a low grown to avoid tipping or cell damage from too high of an initial ET and too aggressive main roasting phase.

I too have not had any consistent results using color as a degree of roast level indicator. Temp works best for me.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
yamhill
Thanks all. This is really good information.

When you all are talking about first crack are you talking about the beginning or the rolling first crack point? I get the beginning of first crack at around 400 and rolling first crack at about 410 to 415. Also of note, the thermocouple is mounted vertically in the center of the popper's roasting chamber with the tip about an inch from the bottom.

John
allenb

Quote

yamhill wrote:
Thanks all. This is really good information.

When you all are talking about first crack are you talking about the beginning or the rolling first crack point? I get the beginning of first crack at around 400 and rolling first crack at about 410 to 415. Also of note, the thermocouple is mounted vertically in the center of the popper's roasting chamber with the tip about an inch from the bottom.

John


Beginning of 1C. There are usually some oddballs that decide to pop earlier (5-10 degrees earlier than the rest) but I disregard these.

If you're getting 1C (start of) at 400 F your getting a good read where it is in my opinion.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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