Posted Tue Apr 3, 2012, 6:12pm Subject: Very uneven roast
I have been roasting with the hg/bm method for about 4 months now. It has been a great experience so far but tonight I got my first uneven roast. I roasted two batches (each 455 gram loads). First batch was very even just like normal i let the bm cool down while i put that batch in mason jars and then started the second roast. This was the first time I tried to do two in a row so maybe that had something to do with it. Any ideas would be most appreciated.
ive never used the heat gun/bread machine method but i think you answered your own question. you probably didnt cool down the BM enough. through more experience/practice, you can probably get good results by changing the way you roast depending on the temp of the drum.
I figured that might be it. I usually let the chamber heat up about three minutes but didn't for the second roast because if the bread machine gets too hot it will shut off. I have been meaning to hard wire it but have not done it yet. I guess I just need to plan on doing one roast at a time from now on.
The first time I tried to do two roasts, back to back, in my Bread Machine (before I had hard wired it) it stopped turning right in the middle of the second roast and the motor would never turn again (even after power off and cool down) until I hard wired it. So I guess it overheated something. It is well worth hard wiring the motor.
Now I do back to back roasts all the time. I don't let it cool down. In fact I spend some time getting it good and hot before I put the greens in. I've never gotten an uneven roast with it. I wonder if your uneven roast has to do with the slow startup kneading action of the Bread Machine when it's doing a standard bread cycle rather than having the motor on full all the time?
The issue comes from the agitation, and without a top my BMHG will only do about 400g reliably. With top the capacity isn't much more than about 500g.
Modifying the bread machine - you're responsible for your own consequences, but good info on homeroasters.org: http://www.homeroasters.org/php/forum/viewthread.php?thread_id=528
Unless your BMHG has a DC motor (and that's up to you to figure out) the motor has a start capacitor.
Somewhere on homeroasters it discusses the temperature thermister - they say if you simply find and unscrew it and tuck it away from the heating chamber, it won't shut off.
Back to the issue, tho: the agitation of the beans with a larger load looks pretty good - at the beginning. Remember, this coffee will approximately double in volume, so when they expand during roasting (right before 1C is the largest expansion, when the chaff starts flowing out of the batch), the depth of the beans end up with striation (layers). It's a lot like overloading a top-loading washer. The beans on the bottom get a bit of heat, the beans on the top head toward 2C before the ones on the bottom barely reach 1C. End result is a mottled mess of unevenly roasted beans because the expanded volume is too much for the small kneading agitator to circulate beans from the bottom to the top.
Solutions include modifying the agitator (a pain), reducing bean load. If you could inject the heat at the bottom, maybe that might be the ticket but a real conundrum for minimal modification of a BM. I've found a bit of help by evenly heating the batch by holding the temperature at around 230°F-250°F early on - before the beans have expanded (drying phase). Once they start to expand, the agitator is unable to circulate the beans from the bottom of the chamber to the top (where the heat source is), but this seems to get enough heat in the batch to get more heat lower into the batch.
Of course, YMMV.
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No, they were not the same bean. The first was for my wife's drip coffee. It was Brazil cerrado fazenda no-name-o from sweet Maria's. This is a bit off subject but I tried to do that roast profile a little bit different and extend the roast by a few minutes. I was shooting for a city plus to full city and made it there in 13 minutes. I heated the roast chamber like i always do during the first three min of the pulsing phase of the bread machine. I then dropped the beans and reduced the temp to about 50% to extend the drying time. I raised the temp gradually as I noticed the color changing. One thing that I noted though was that there was not much of a first crack. This is the first time I tried that bean so I am not sure if that is normal.
The second roast was sweet Maria's monkey blend. This roast I did not heat the roast chamber but I didn't drop the beans until after the three minute pulse of the bread machine. Everything looked normal until I poured the beans in the colander to cool them. I hit first crack at 8 min 48 sec which is normal for most of my roasts. Pulled the beans right befor second crack at around 11 minutes.
I never have attempted a load more than 455 grams and don't plan to. I think I will work on hard wiring the bread machine and getting some thermal couples in there so I can have a better understanding of what is going on. Thanks for the help. I really appreciate it.
My guess is it was more about the second roast being a blend(though I have no experience with Monkey). Pre-roast blends can be designed to taste good but not necessarily look even. There may also be a component in the blend that has some quakers.
Bingo; different coffees roast differently, so blends will look uneven. SM built Monkey to be roasted in this fashion, which is why they ship it to you already blended. Trust your taste buds here. As a starting point, I believe you'd be rewarded well for taking the current Monkey right up to FC+, and I mean the second you detect 2nd Crack, cool it.
I've roasted a ton of Monkey in the old BM so here's what help I can offer. First, like you said, getting a bean temp TC in there will really help you out with your profile. You will have some roast level variation with the monkey as said above it is a preroast blend so each bean type will roast slightly differently. There should not be a large difference in roast color with the Monkey. 455g load is fine. My first recommendation would be to let the monkey go into 2c maybe 15 seconds or so - the cup will be better IMHO. You also should try to lengthen the 1C to 2C time. Once I hit 1C (400F) I try to keep the roast progressing at 9F/min. A longer 1c to 2C time will also let the "slower" beans catch up and even the roast a bit more. It's also worth culling the beans preroast - blends have more likelihood of higher number of bean defects that will give you quakers or overroasted hollow beans.
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