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Homeroasters.org » THE ART OF ROASTING COFFEE » Roasting Coffee
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The well tempered roaster
renatoa
Discovered recently a post by Jim Schulman that was a revelation for me, after two years of roasting experiments.
This simple sentence summarize so perfectly the essence of what a roaster should do, that I am amazed it is not engraved as a motto for any roasting coffee related site.

"If there is one thing that somewhat works for all roasters, it's that a good roast requires that the ET follow a certain profile, and stay within certain limits, so the beans don't under dry, over dry, bake, scorch or tip.
Basically, this magic profile is a starting temperature of around 325F to 400F (163-204C), and a ramp up to around 450F to 480F(232-250C) in around 6 to 8 minutes, and holding it steady there to the end of the roast, whenever that may occur.
This ET part is basic roasting chemistry, and the same for all roasters and coffees. But the heat inputs required moment by moment to achieve this ET curve is based on the roaster's thermal characteristics, and is different for every roaster design. "

http://www.home-barista.com/home-roasting/timing-first-crack-heat-reduction-t11144.html#p127194

Why is this so important for me... because is about ET, not BT ! because I gave up to fight finding the method of accurate BT measurement... it simply don't exist !
And I say this as a computer/automatics engineer, since 1985...
The mix of beans and hot air is simply too chaotic to rely on any measurement method for predictable, repetitive and accurate results.
More, using this information (BT) to drive the process is simple lottery.
Conversely, measuring ET is so simple and precise, that the JS quote become a gem in this field.
All I can say is wish finding that statement two years ago...

End of rant, stone beat start :)
DIY: TurboOven, Popcorn
Moded commercial: Dieckmann RoestMeister, Nesco
PID/ramp/soak controllers
 
oldgearhead
Renatoa - I have a temperature probe located 1.5 inches below the perf plate that has done an excellent job of keeping track of the air temperature. The probe at the start of the roast IS influenced by the bean temperature and at the end of 12 minutes it is a very accurate indication of roast level. Throughout the roast I use this temperature probe to maintain a good indication of an ever increasing ROR. In fact I removed all other temperature probes 5 years ago... but I do not use PID temperature control..
No oil on my beans...
 
renatoa
oldgearhead wrote:

...that has done an excellent job of keeping track of the air temperature.
...
but I do not use PID temperature control.. [/size]


Yes, is what I said, air temperature is by far easier and precise to measure than beans...

Me too I gave up with PID in the last months, the cheap controllers are unable to cope with fast changes of air flow temp.
Manual PWM give me the best results.
DIY: TurboOven, Popcorn
Moded commercial: Dieckmann RoestMeister, Nesco
PID/ramp/soak controllers
 
oldgearhead
You will discover that if the probe is mounted close to the perf plate, the resulting reading is NOT entirely air temperature because the room-temperature greens have a big influence on the reading when introduced...
I use NO temperature control during a roast. I simply set the %on time of the heater based on the ambient air temperature. However, my roaster mixes roast chamber exit air and ambient air at the blower inlet.
This is what allows me roast 500 grams of greens with as little as 1.1 kw of electric heat..example: this weekend I expect 16 C temperature in the garage, so 95-16 = 79, 1550 x 79% = 1224 watts for 425g loads, I have a slightly different equation for 500g loads....
No oil on my beans...
 
jkoll42
renatoa wrote:

Discovered recently a post by Jim Schulman that was a revelation for me, after two years of roasting experiments.
This simple sentence summarize so perfectly the essence of what a roaster should do, that I am amazed it is not engraved as a motto for any roasting coffee related site.

"If there is one thing that somewhat works for all roasters, it's that a good roast requires that the ET follow a certain profile, and stay within certain limits, so the beans don't under dry, over dry, bake, scorch or tip.
Basically, this magic profile is a starting temperature of around 325F to 400F (163-204C), and a ramp up to around 450F to 480F(232-250C) in around 6 to 8 minutes, and holding it steady there to the end of the roast, whenever that may occur.
This ET part is basic roasting chemistry, and the same for all roasters and coffees. But the heat inputs required moment by moment to achieve this ET curve is based on the roaster's thermal characteristics, and is different for every roaster design. "

http://www.home-barista.com/home-roasting/timing-first-crack-heat-reduction-t11144.html#p127194

Why is this so important for me... because is about ET, not BT ! because I gave up to fight finding the method of accurate BT measurement... it simply don't exist !
And I say this as a computer/automatics engineer, since 1985...
The mix of beans and hot air is simply too chaotic to rely on any measurement method for predictable, repetitive and accurate results.
More, using this information (BT) to drive the process is simple lottery.
Conversely, measuring ET is so simple and precise, that the JS quote become a gem in this field.
All I can say is wish finding that statement two years ago...

End of rant, stone beat start :)


I think a lot has to do with the roaster design. I only measure BT and I'm just using a twisted TC (not even welded). I've consistently been hitting 1C at 400F +/- a degree F or two for years. 2C has a slightly larger range but that just has to do with bean variations. I'm not discounting your experience with your roaster but for me and mine I get consistent BT readings.

The biggest switch for me was when I started roasting based on Rate of Rise as opposed to temperature. Way easier! I'll likely actually cry when the Arduino/Artisan setup eventually craps out.
Edited by jkoll42 on 04/05/2017 12:51
-Jon
Honey badger 1k, Bunn LPG-2E, Technivorm, Cimbali Max Hybrid, Vibiemme Double Domo V3
 
JackH
@Renatoa

I have also read a study funded by Nestle I think. I have a link to it and will post it when I find it.

The only reason I monitor BT is to see how close I am to first crack. This seem to be a repeatable value.

Keep my ET at no more than 500F and avoid roasting longer than 15 minutes. I control the heater manually on my KKTO roaster (600- 700g).

I find that the heat reductions I do to maintain ET also seems to control the rate of rise at just the right time. This works for me and my roaster.
---Jack

KKTO Roaster.
 
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