Well, this is my extreme roast, a charge BT of 500F! jeje

Beans = Ethiopia DH Haile Selassie Sidamo from Sweet Marias
room temp = 71F
load 200 grams
charge temp = 500F
MET = 560F

5:58 390F 1C
(at 400F turn off power to SSR. MET starts to drop. Then MET meets BT at 430F)
8:27 429F END

Differences: I was force to turned off the SSR power at BT 400F, otherwise the roast would have ended too early.

Red line = BT
Green line = Exhaust T at handle
Purple line = BT - ExhT

(I forgot to turn off the data logger at the end of the roast, so you see a long decline of T at the end.)




Preliminary chewing results: The results are so so because there is a little char flavor. At first byte, I sense a char shadow on some of the beans, but then the flavor changes in to something else. Some beans have some initial char flavor. The total flavor is very different from previous roast (charge temp of 420F no char flavor). I am not able to say how this will transform in the cup. Maybe a charge of 500F is too much but 420F is OK.

Cheers

Cheers

Thanks for posting your experiments! I just got back from a short trip and I'm looking forward to doing more roasting and cupping... I'm still blinking (with astonishment) after the last blind tasting I did!

I'm thinking now that the point at which a roast is ended has a much more significant affect on taste than the amount of time it takes to get there.

Regards, Henry

Hi Henry.

I have done a very few number of roasts limiting the MET, but this is what I've found so far.

I used to do fast roasts (unaware of the MET limits) to mimic profiles and times, expecting maybe to see defects visually. I thought the results were Ok but the flavor was tainted with what I was calling at the time 'redishness' (espresso only). But since 'redishness' was some kind of acidity, I thought it was natural to the beans. It was like an acrid taint that I thought it was due to the natural acidity of the beans. In that respect I thought, hmmm, maybe these beans are better at light roast (low heat). But after a few roast controlling the MET, I've found that the chewing char flavor will transform into acridness/bad-acidity in the cup. Now that I roast only by controlling the MET, my cups don't have unpleasant acidity. They do have acidity, but it is widespread and pleasant and transparent. This has been an important eye opening experience for me.

But the char chewing flavor is not completely bad. In light moderation, it can work by spicing up the cup.

Cheers

All these posts make me want to add more control to my hottop! I'm currently running the heating element off a variac, and playing with batch sizes between 150 and 200 grams. I find that at 150g, I have very precise control over the roast. The roast is not just one giant concave curve, but i can really do what i want with it. At 200g, i lose a little control as the roast will tend to "coast" in the direction it is already travelling. But with more bean-to-bean, and less bean-to-drum, i find that the roasts are slightly better. Lately I've dropped back down to 180g. This allows me to finish the roast with a MET of 440F and a BT of 205-215F (for espresso).

Here's one of my better roasts at the old 150g size. It got away from me a little at the end. I'm gonna add an additional fan so i can better control the finish. the solid lines are what i intended (although I ignored the solid blue because i knew from a previous roast where i wanted ET to be) the dotted lines are the datapoints for BT (red) and ET (blue). I want to try to vary each section of the roast from convex to concave and see if that has any effect on the roast. My other question is whether there is are particular temperature ranges to speed through and others to dwell in (apart from lengthening first to second crack - you can see i adjust my slope down to 5-10 degrees / min for that period).

another_jim wrote:I have a very good reason for monitoring any version of the ET that will tell you whether you are approaching the ash zone. I've just cupped the last of about a dozen professional roasts, some from the best roasters in the country, and every single one of them from a winter area is ashy (the ones from Hawaii are fine). I asked around about this. In the winter, the ventilation air on the roaster tends to be at a lower temperature than usual. The roasters are running fast profiles, and are trying to maintain the same roast timing. As a result, they are exceeding the upper limit of drum temperatures and are ruining the coffee (at least for me).

There's no point in finishing your roast in exactly 12.5 minutes if it tastes like it's been dipped in coals.

I am just now reading this thread as my winter roasts especially for espresso have defined for me at least what ashy taste really means. I will try going a bit slower and see if I can regain the balanced roasts I've obtained before winter cursed us here in NY.

Thanks for that bit of insight!