another_jim wrote: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.

Great food for thought! MET/ET is the key

From a roast of 640g this afternoon. What surprised me the most was the almost flat MET.

notes: the roast was basically a big mistake in that I started with air at 100% drum - something I've never done before and did not intend to do. Drum temp was stabilized for 3" before dropping the beans in. The air flow was at maximum from the start and profile control was done with gas alone. Unfortunately I'm not going to get to taste the roast as I gave it all away at a Christmas Eve dinner

Question for y'all: I noticed in the 4 roasts that I've posted that the 2 with flat METs (1,4) were started after stabilizing the drum temp, while the 2 with extreme MET variation (2,3) were started without stabilizing the drum temp (ie just dropping the beans in and 'turning' at a certain temp). Has anybody noticed the same pattern in their roasts? Is it possible to have a steady MET without stabilizing beforehand?

Arpi wrote:This is the graph I got

Arpi, in the graph you posted what are the green and purple lines? It looks like PID'ing the ET worked out really well for you!

another_jim wrote: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).

Wow...quite a revelation! How did the roasters you talked to about this respond? I guess the only options are to roast in a temp-controlled facility (a bit of a challenge with the amount of airflow needed to exhaust the smoke) or accept doing longer roasts. My roasting area is 12C (going up to 16C after an hour of running the gas).

Can you describe the ashy taste in some other ways? Does it occur even at early 2nd roasts? I've had a few roasts that had an appealing smoked fish/meat aspect - do you have any positive culinary references for the ashy taste you're getting?

Regards, Henry

Ashy means an aftertaste like ashes or charcoal. It can happen at any post 1st crack roast level, since it is damage to the bean from an overheated drum or from direct exposure to radiated heat. Tipped roasts will alway taste ashy, but there doesn't need to be any visible damage for the taste fault to be there. Like all taste faults, it is most apparent when the brewed cup is left to cool (about 20 minutes after pouring in the water).

A fast roast done in an over hot drum or uncontrolled popcorn popper can end up tasting both ashy and grassy. This is easy to avoid if you don't mind flattening the taste; but if you want the taste to pop, you need to roast close to the speed limit. Hence that bad cupping result.

According to the various articles by Staub and Boot, the upper limit for high grown coffees is 520F, and for low grown around 480F. The numbers need to be taken with a large grain of salt, since the temperature gradient from gas flame or red hot electric element to the bean is going to be extreme, and even small changes in the measuring will make a big difference. I think the only way to calibrate is to do straight line MET profile roasts of a DP Brazil to a medium level and spot the temperature when you can just detect a ghost of ash. You can run higher until the first crack, since there's still moisture in the bean. I think the damage happens mostly in the glass phase, when the beans expand quickly in the second half of the first crack.

OK. I did another roast. This technique from Jim seems to do wonders as it is very effective and does an excellent job. BIG THANKS.

This time I drop the MET from 600F to 575F, but I also increased the drop temperature by 50F. The resulting total time was about the same but I think the flavor improved substancially. The last roast had a little charcoal byte to it. I attributed it incorrectly to the roast level. It didn't show in the espresso machine but it did show a little went chewing the beans. I still have the beans from the first batch and I can tell a big difference went chewing both beans one after another.

The PID does an excellent job. Before hand, I auto tuned the PID to the new configuration. The PID kept a constant +-5F. It acted fast to changes. No lag measuring ET as opposed to the huge lag of the BT.

On this new roast, the data logger turned off by itself in the middle of the roast

This is what I got:

beans: Burundi Bwayi lot #5
load: 200 grams
fan: 5
power setting: PIDed constant ET 575F
No power or fan adjustments made

room temp = 70F
0:00 drop beans at 350F (BT then dropped to 220F)
6:55 1C starts 383F (and last for < 3 mins)
10:48 2C 430F END

This time, the sound volume of 2C was like rice krispies, whereas in the other roast, it had louder pops. This means that in the later roast, the curve of graph had a smaller slope approaching 2C.

(picture with different light as previous pic, cloudy day, not sunny + my window is tinted)


This roast was an improvement from the last one in terms of chewing taste. Very promising.

Cheers

PS: the other lines from the previous graph was other thermocouple of the data logger connected but with no important meaning. They were the exhaust temp and the difference between the BT and Exh T but it was placed in a very bad location, so it wasn't important.

OK. I could not wait for a couple of days to cup the newly roasted coffee.

Burundi Bwayi lot #5

I know I should wait but I did a shot at 198F. It had a creamy flavor, nasal, kind of like eggnog. Distant aromatic notes. Thick body.

I did another shot at 205F but it was worse than the 198F. Here the brightness was dominating and it was hard to see through.

The 198F shot reminded me somehow about Yemen beans.

In comparison with the previous roast, the new cream flavor was dominating, whereas it was lacking before. Previous roast had a broader higher pitch. Color wise, both roasts show the same color (roast degree) but the taste is very different.

Cheers

At +/- 5F, Your PID is doing a much better job than I can do manually with the ET.

On the taste side, I'm embarrassed to say that I couldn't pick the odd one out in a blind cupping of the first and second roasts (up in my first post). There were two samples of the first roast and one of the second, and in spite of the pretty extreme different between the two roast profiles I wasn't able to identify the lone second roast...

I hope this is a skill that can be developed!

Regards, Henry

Maybe if the roast is very dark they get a 'roast' flavor. The flavor in my two roasts are day and night, even the smell. Chewing the beans one after another will give you a better comparison, as the flavor does not depend on brewing parameters.

The complexity of roasting has been dramatically reduced thanks to Jim. For me, now there are only two roasting variables.

A = drop temp (controls time to 1C)
B = MET (controls time from 1C to 2C - feathering)

Dropping beans at a higher T (within limits) will get you sooner to the 400Fs. And keeping a higher MET (within limits) will also speed up the roast at the end (less feathering) as the difference between BT and MET are greater. So if I want a long very feathered end (long time from 1C to 2C), I lower the MET. The decreasing difference between BT (going up) and MET (steady) does the feathering automatically without touching anything. I've only done two roasts so far, but I guess it will work that way. Plus, bounding MET will prevent from entering charcoal territory.

The PID did the autotune fast (<5 mins). That meant that it got cooler and hotter fast. For comparison, the BT autotune took something like 30 mins. During the roast at 575F, the LED was doing very uneven pulses. Sometimes very long, sometimes very short, which made it look as if it was doing a good job. In an espresso machine this is not the case because of the less changing circumstances. My probe was laying on the bottom 3/4 deep from the hole, with the tip towards one heating element, keeping the same distance away than the drum is also from the heating element. I guess that laying on the bottom, closer to the air intake, makes it cool faster. My thermocouple wire is not very long, so I could not have put it anywhere else.

In my PID I can select from a palette of 7 SV values without need to go up or down with the arrow. I can have one setting for warming up the MET to 250F,300F,350F, fully warming the roaster without beans, and then use other for roasting at 525F, 550F, 575F.

maybe a light roast would look like this: MET 250F then at bean drop change to MET 525F

Cheers

Small update.

i tried this morning the coffee roasted yesterday and the cream flavor was gone. The cream flavor must have been an artifact of too fresh coffee.

I did two more roasts and then I found something important in the new Roast Magazine. These are the two roasts.

Beans: Sweet Marias Ethipia DP Haile Selassie Sidamo



This is the second roast, trying to get a grip of how much drop temp does. Same MET of 560F



second roast was better by chewing the bean. First one was missing notes and flatter. A shorter roast time was better. Looks like higher charge Ts lift the beginning of the roast line, reaching 1C faster but also possibly lengthening the time between 1C and 2C. When MET is the same, the line would have a flatter slope. The second graph is flatter than the first one.

After I do my tinkering, I open the new arrival of Roast Magazine Jan-Feb 2010.

In page 62, the roaster from Counter Coulture, Timothy Hill explains that to preserve the coffees fruit notes of Guatemala HueHueTenango, he charges the coffee at 420F But then he states that this roast lasts 14:30

I wished I had read that before I did these two roasts. Here I am dropping beans at 300F and 350F with fruity beans Anyway, the second one came out more fruity than the first. But now I am wondering what flavor would I get with 420F (70F higher)

No more roasting for me till next weekend

Hi!

This is the same roast as before (constant MET of 560F) but with a charge temp of 420F!

Surprisingly, everything looks normal. No damage what so ever to the beans. Beans have a pleasant chewing flavor with absolutely no deffects. Different beans have a slight different flavor (it was the same before also). The main difference between roasting under char flavor limits (low MET) is that the chewing flavor has no notes of being acrid or chared.

Beans = Ethiopia DH Haile Selassie Sidamo from Sweet Marias
Load = 200 grams
Room Temp = 68F
MET = 560F
Charge Temp = 420F
1C = 8:11 388F
10:36 427F END

This roast was done from room temp with no warming time, straight to a charge BT of 420F. Good results.





Due to the linearity of the roast graph, it looks easy to play with geometry to anticipate times. Maybe turning off the PID control after say 400F would let the roaster coast into a feathered edge. But the purpose of these roasts was to try to understand the profile of a constant MET (which has the advantage of not damaging the flavor if it is bellow a certain limit)

Cheers

PS: Next roast, a charge > 420F. Heck, why not?