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New HG/BM roaster - frustrated
A little background: I started roasting around 2 months ago. I started with the HG/DB method, but even though my coffee tasted ok I wasn't satisfied with my results/batch size (it always looked quite uneven). I switched to the HG/BM method, picked up a BM at the thrift store for 5 bucks, rewired it, and did a little modding, mostly following seedlings setup. I removed the sight glass, made a foil gasket for the HG, made a hole in the rear of the BM for chaff to exit, and drilled a hole in my BM "bucket" for a thermocouple. I'm using the orange Harbor Freight heatgun and router speed control to manage temperature. My first roast didn't go so well - unfamiliarity with the setup = burnt beans. The next several, however, were great. Very even roasts, very good tasting coffee. Things did not stay that way though, hence this post!

My last 4 roasts have been undrinkable. The first 2 I ruined were a lb each of 2 of the Colombian microlots SM had available in May. I tried to keep them very light per Tom's recommendations, and thought I did a good job... until I tasted them. They were extremely bitter with almost no flavor at all. I tasted them every day for 10 days straight hoping they would improve with rest, but they did not. The same thing happened with the lb of Kenya I had left, a coffee I had previously roasted and had good results with.

I then ordered some more beans, deciding to just keep at it. They came in this week, and I did my first roast on Tuesday evening, 1 lb of SM's Costa Rica Finca La Ponderosa. My results are a little different than before, but still undrinkable. It tastes very bitter, slightly grassy, with almost no coffee flavor to it. I don't understand what I did wrong. I made sure to log my temperatures this time so I could ask for pointers in case I botched yet another roast, and here they are (in celcius, my thermocouple does not do fahrenheit):

Preheat a few minutes, thermocouple read 172C when I dumped beans in.

1:00 - 85 ("medium" heat, router speed control at ~75%)
2:00 - 103
3:00 - 114
4:00 - 129
5:00 - 142 (I believe I turned the heat up at this point)
6:00 - 163
7:00 - 184
8:00 - 197
9:00 - 208 (FC begins, heat turned down)
10:00 - 212
11:00 - 216
12:00 - 223 (Pulled shortly after this, looks like a good City+ to FC roast)

The beans look beautiful. Very even roast, no defects I can see (tipping, etc). But as previously mentioned, they taste awful. I have tasted them every day since roasting, with no noticeable change in flavor.

What am I doing wrong? I don't believe my roast stalled, I was watching temps like a hawk since I do not want to waste more coffee, they never went down.

Am I trying to go too fast? If so, which part of the roast should I try to stretch out? Drying? Ramp to FC? FC to end of roast? Any advice would be much appreciated, I have 9 more lbs of beans staring me down and I don't want to ruin them!
Greetings and Welcome!

Sorry to hear you're having difficulty. Where do you have your temp sensor, and what type is it? Please describe your TC - bead-type / fast, or slow? Location?

Are you saying that only the light roasts taste bad? If you were to do a roast to 2nd crack, would it taste good?

How are you brewing the coffee? Maybe a de-scale is in order? Using filtered water?

I enjoy a light roast sometimes, but in my experience it is more difficult to achieve. I use a popper for light roasts. The key, I think, is drying time. I'll use F since that's what I remember: 4 minutes to 300F/150C, another 4 to 1st crack 400F/205C, and then 2 to 4 minutes depending on how light I choose to go. I can't achieve the rapid ramps required for a light roast, in my bread machine yet. You need 30 F per minute ramps to do it I think. In the popper, my batch size is smaller but then again my mistakes don't waste as much coffee either.

My BM/HG roasts are usually into 2nd crack, at least briefly - audible, and smoke, and temps. They run 15 to 17 minutes.

My two cents: go back to what you were doing - get the coffee tasting good, and then work on improving your roaster so it can achieve steeper ramps. In my popper I've done good tasting light roasts even though I stopped at 420F/215C. The key is drying time- getting to 300F/150C in 4 minutes or so. -bill
Edited by bvwelch on 06/12/2010 7:33 AM
My thermocouple is a cheap K type that comes with the Cen-Tech multimeters at Harbor Freight. It seems to respond quickly and accurately. I have it placed in a corner of my BM pan, high enough to clear the paddle but low enough to still be completely covered by beans even when they are not expanded. I'm brewing in a CCD, boiling filtered water in a stovetop kettle, it has no scale buildup in it.

I'm not sure if only light roasts taste bad, I have not tried to take one dark because I prefer lighter roasts. I'm pretty sure my setup could pull off the temps you described for a light roast if I used a slightly smaller load. Maybe I should give that a shot?

I would go back to what I was doing but I did not take any notes on my successful roasts. I thought I WAS doing it the same way, except I am now controlling temp better after/during FC and stretching it out a bit. I thought that was a good thing?

Thanks for the advice!
clr, I'm as confused as you about why the roasts aren't turning out - the numbers seem good (unless your probe is reading high??). I'd say you need to be completely sure first crack has finished.

How do you cool the beans? Granted, you're cooling the same way you did with good roasts I assume.

On my router speed control, I start the roast at about 2:00 (on a clock face) for a couple of minutes, then go to 3:00 until just prior to first crack, then spend thirty seconds backing down to 2:00 through first crack, then start creeping back down to about 12:00 to extend time between first crack and second crack. First crack usually comes between 9:00 and 11:00, and add 4 minutes to start of second crack.

Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
I have probably the exact same meter from HF and it has worked well for me for a couple years now.

Here's one idea you could try without changing your setup -- when you get to 300F/150C pause there for one minute, possibly two minutes. The idea is make a light roast that is possibly a little 'baked' but drinkable, then try shorting this time to make the coffee brighter but not grassy/grainy.

If you decide to reduce your load, you may need to put your probe lower. Mine is very low, and in the corner (thanks CHAD) so the paddle can't possibly reach it.

I like reading Jim Schulman's posts over on HB about profiling and light roasts. Here is a thread -- scroll way way down to where Jim has a plot of an 11 minute, Panama Elida roast. http://www.home-b...11876.html
Edited by bvwelch on 06/12/2010 11:48 AM
seedlings - I'm fairly sure FC has ended in my roasts.. but I'm definitely not positive. My setup is fairly loud and while I can definitely tell when FC has begun it's kind of hard to keep track of it with all the noise. I will be sure to listen very closely to my next roast. As for the probe reading high, it seems to work fine reading room temperature and such so I'm not sure that is an issue. Those settings on the router speed control are pretty close to what I use, though I have not taken it quite that low post FC.

I cool them with a bucket/colander/shop vac setup, they are cool enough to touch within a minute, and within 3-5 they are done.

bv - I may give that a try, thanks. I'll check that thread out as well and see if I can pick anything up from Jim's posts.
If the beans 'look good' but taste grassy, it probably means they are somewhat raw on inside. How's the color look after being ground?

Longer drying time should help. Smaller batches may help too.
They look fairly close to the color of the whole bean when ground - perhaps a bit lighter. I will most likely do a roast this evening. I plan on trying out a slightly longer drying time, and making sure to listen very closely to FC to ensure it is done.
Edited by clr on 06/12/2010 12:53 PM
I think what CHAD meant was - is your probe really measuring bean temp or is it getting hit by direct HG and reading out a number that is higher than the beans. Easy enough to tell -- if 1st happens (audible) around 385-400 reliably, then that's a good indication that your probe is in a good spot, for the given batch size that you're using.
Edited by bvwelch on 06/12/2010 4:41 PM
Ah, sorry. Yeah, I generally start hearing FC around 200-208 celcius, which is in that range.
I think I have fixed the grassy taste problem. I'm not sure but I believe seedlings was correct, I don't think I was letting FC finish in my lighter roasts. I never made sure to listen to the cracks, I paid too much attention to temperature.

I decided to try out a darker roast, and went with a lb of Guatemala that Tom's notes say is nice from City all the way to FC+. I did not control temp as well as I would have liked towards the end of the roast, and I ended up with some tipping and craters in my beans. Second crack was going as I dumped the beans. The grassy taste is definitely gone though! I do detect some "burnt" taste to it, but that is due to my aforementioned poor temperature control I'm sure.

Thank you both very much for the help! I hope this little revelation fixes my light roasts as well.
All my roasts that are bitter and grassy tasting are as a result of under roasted coffee. I can definitely hear first crack.

In my opinion, if you want a reference for mega light roasts, try some of PTs coffee new offerings. They're based where I live, and I just can't drink their coffee. Most of it is bitter to me, but they have started roasting extremely light, and that might give you a base for some self evaluation. Their coffee isn't grassy or green tasting, just too bitter and almost sour to me. I prefer a roast in between first and second crack most of the time.
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