comments on roast temps / time

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comments on roast temps / time

Postby Joris » Sun Jan 11, 2009 3:20 pm

OK, here's the problem. I used to roast with a Gene which measured temps of exit hot air afaik. Then I roasted a wile on a homebuilt roaster without temp measurements. Now I'm roasting on my new roaster which has 2 points where the temp gets measured. One probe is in the beanmass, the other just below the drum, a bit left so it's not directly above burner.

I've done a couple of roasts now and used Greenbean's nifty app to log them.

The roasts were all a bit uneven, so I'll speed up the rpm of the drum so the beans get mixed better.

I started roasting, gradually adding more heat until I got at a chamber temp of about 255. I kept it there untill 1th crack started (about 188 beanmass) at which point I left the burner on that level. A bit before 1th crack I noticed a drop in chamber temp, for which i compensated with som extra heat. It then was steady until start of 1th. The chamber temp rocketed as soon as 1th crack was rolling until it reached a 289 at start of 2nd.


Time is in minutes, CT = Chamber Temp, BT = Bean Temp
Am unsure on how accurate the temperature of beanmass is.
Amount roasted 1Kg

Time......CT.........BT
0..........8.............8
1..........100.........18
2..........170.........37
3..........206.........58
4..........231.........78
5..........236.........102
6..........250.........120
7..........256.........136
8..........257.........152
9..........257.........166
10.........257.........179
11.........258.........188
12.........262.........200
13.........288.........209
14.........290.........221

1th @ 10m48s, CT 257, BT 186
2nd @ 13m20s, CT 289, BT 218
Dumped @ 14:00

Result: too dark, shouldn't have taken them 40s into 2nd :shock:

All in all I got the feeling roasting time was quite short and the time between 1th and second was short as well.

So what's the time between 1th and 2nd on other drum conduction roasters, anyone ? How long shoul such a roast take in total ? Is there someone who could tell me why the chamber temp dived before, and rocketed at 1th crack ? Any comments on my profile in general ?
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RE: comments on roast temps / time

Postby lukas » Sun Jan 11, 2009 8:10 pm

Greenbean's app is superb, no?
I have some suggestions from reading and my own experience:

* temperature falls right before 1. because the most if water is already vaporized in the beans, and they start to 'suck' the available energy up
* with adding more heat, you effectively got 1st crack going faster
* 1st crack is an exothermic reaction, so the beans give heat to the environment and temperature rises faster (in drum roasters, you can compensate (if you wish) by giving less heat for a period during 1st crack)
* in drum roasters, don't underestimate 2nd crack. it will go fast and come unexpected (at least for me as a stove-top roaster ;)

I'd suggest cupping your coffee :) and depending on the result, go for a later 1st crack, take a little heat away during first crack (for 10-50 seconds, depending on how your roaster behaves) and give 'normal' heat until you reach second crack (if you wish so).

Oh my, did I really make all that up? I have no idea what I'm talking about, that's all my gut feeling here! I'd so love to give that roaster a try and also sample your roasts, Joris!

And don't forget to give it the time it nees for you and your new roaster to become good friends :)
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RE: comments on roast temps / time

Postby Joris » Sun Jan 11, 2009 8:39 pm

Thank you Lukas, that clarifies soms things. And about testing the roaster, you know you're more than welcome over here.
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RE: comments on roast temps / time

Postby bruceb » Sun Jan 11, 2009 9:36 pm

A few weeks ago I did my 1000th roast on the HotTop. That's 230 Kg of coffee, so I had a little celebration and roasted the 1001st, some Mexico Maragogype. But I digress:

On the "Digital" Hottop (not the programmable model) it takes about 17 minutes to get to 1st crack. Depending greatly on the beans being roasted 1st crack lasts for about 45 seconds followed by a pause of roughly 1 minute of silence at which time 2nd crack begins (about 1 min 45 seconds after the end of first). From the first single pops of second crack to rolling second crack it takes roughly 15 seconds at which time the temperature in the air stream is about 208°C).
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RE: comments on roast temps / time

Postby Joris » Sun Jan 11, 2009 10:10 pm

So my roasts are on the short side.
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RE: comments on roast temps / time

Postby lukas » Mon Jan 12, 2009 12:44 am

And I'd consider 17 minutes to 1st crack to be on the rather long side, but this will vary greatly from roaster to roater (and method to method). Congratulations Bruce, that's quite an amount of coffee there! Do you buy your yearly coverage in standard sacks now? :)
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RE: comments on roast temps / time

Postby CakeBoy » Sat Jan 31, 2009 6:37 pm

Yes indeed, crikey Bruce that is a fair load of coffee in the hottop! :)

For what it's worth/in case it's of use (as it's also a gas roaster and therefore fairly similar to Joris' machine), the Pinhalense varies a little in timing from roast to roast - partially I expect because of the manual gas settings and ambient temperature flutuations (it can be very hot/cold out there). anyway, a typical roast, dumping around 2C, is in the region of 14 minutes with an approximate temperature measurement of 225-230C measuring the moving bean mass with an infrared temperature 'gun' (so accuracy can vary, but it's the best method available to us).
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RE: comments on roast temps / time

Postby Joris » Sun Feb 01, 2009 8:04 pm

Thanks for the info cakey

••mental note to self - borrow IR thermometer to dubbelcheck sensor readouts••
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Postby ivdp » Sun Feb 15, 2009 7:24 pm

Roasting time: not very standard, some pro's like at least 20 mins, some go for 12 minutes.
Some roast dark, some light.
If you lower temp at first crack you have a longer rest period before 2nd and can roast longer in 2nd crack without burning your roast.
A lot of variables and roasting possibilities . . .

Your temp seems a bit high. More than 220C should not be necessary.
Of course a small light chamber acts quite differently than a larger heavy chamber.
Gas or electricity also act differently.
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Postby Joris » Sun Feb 15, 2009 9:54 pm

Thanks Ivo, i dis some more roasts, after changing some things on the roaster. Will post details tomorrow when I can use a proper keyboard in stread of my phone.
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