Confused about BT during crack

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
Coffee Cougar

#1: Post by Coffee Cougar » Nov 09, 2019, 3:49 pm

I have been roasting on my Quest M3s for a few months now. Prior to starting my coffee roasting adventure, I have been reading and learning a lot from forums like these and videos on YT. From these sources, I have learnt that during first crack the beans release a lot of temperature and the BT reading might increase rapidly.

On my Quest I am getting very different readings, however. Prior to first crack my ROR increases slightly and in to first crack the ROR decreases rapidly. As soon as first crack has finished the temperature rapidly rises and continues to rise during second crack.
Could anyone explain why my results are so very different from what I have read? I am consciously keeping my heat and fan consistent throughout the roast, so that cannot be the cause.

The image shows the roast of 150g of Uganda Bugisu. I also noticed that my turning point takes place very early, though let's stick to one question for this topic.

Image

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Almico
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#2: Post by Almico » Nov 09, 2019, 4:01 pm

There is a 7 page thread 4 posts down discussing this very issue.

Your graph is a perfect example of a "natural" roast, where no heat adjustments are made throughout the roast.

"Nonexistence of Heat Momentum"

Your goal is to learn how to control your roaster to achieve an RoR curve more like this:

Image

Maybe charge lower, but with more heat before dry-end to remove some sag. Then turn the heat down prior to the plateau before first crack and down even more to stop the rise at the end.

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civ

#3: Post by civ » Nov 09, 2019, 4:13 pm

Hello:

Welcome to HB.

I see you are new here so I'll take the liberty to (very emphatically) recommend the use of the search function before posting a question.
Nine out of then times you will see that the question you want to post about has already been asked and answered a few times already.

Edit:

Had you done so (many new members do not do this and it is rather frowned upon) you would have undoubtedly come across |> many posts with questions, answers and opinions with respect to what you are seeing in your RoR curve.

The most recent being <| this long-ish thread which verses on a subject that has been hotly (pun intended) debated many times, here and in other coffee/roasting forums:

"Nonexistence of Heat Momentum"

Check it out, read it over a few times till you can digest it comfortably and then see what you can make of it.

The members who have posted there really know what they are talking about and you will find that within that thread there are two or three possible answers to your question.

Cheers,

CIV

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Peppersass
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#4: Post by Peppersass » Nov 09, 2019, 7:21 pm

With all due respect, I think the 7-page thread referenced is somewhat advanced, somewhat contentious, somewhat irrelevant and somewhat rambling. In other words, I think it's a bit much to ask someone who is relatively new to roasting, and who has a small electric roaster, to wade through all that stuff for an answer.

That said, the second half of Alan's post provides useful advice. You're looking for more of a gradually descending RoR throughout the roast, and typically this means you need to begin reducing the heat before 1C. Since the Quest responds more slowly than a gas roaster, typically you have to start lowering heat 1-2 minutes before 1C.

It would help a lot if you configure Artisan to show your MET curve. That way we can see what you're doing with the heat. It's also important to know the location of the probe that's setup as MET. Is it in the stock ET position or outside the drum? And where is the BT probe? Is it in the stock BT position or in the door next to the sight glass? What kind of probes are you using?

As for the TP time, it looks normal for the Quest. It's really an artificial thing anyway. The bean temperature isn't actually dropping after you charge. What happens is the BT probe cools off when you drop the beans on it, and it takes some time to come back up to equalize with the the outer temperature of the beans.

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civ

#5: Post by civ » Nov 09, 2019, 8:01 pm

Hello:
Peppersass wrote: ... a bit much to ask someone who is relatively new to roasting, and who has a small electric roaster ...
You're quite right.
Mea culpa for not being clearer as to the point I was attempting to make.

I have edited my post to adequately reflect what was my original intention.

Thank you for pointing this out to me.

Best,

CIV

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drgary
Team HB

#6: Post by drgary » Nov 09, 2019, 8:49 pm

Hello Job, and welcome to H-B!

There's a thread that covered the idea of a rate of rise crash, followed by a flick, here:

"What is Baked Coffee?" - Rao

Alan (Almico), above, has been very active posting about that phenomenon and his suggestion at the end of his post is a short-cut on how to address it. If there is a crash in rate of rise it is followed by a rapid rise, or "flick." Roasters here who have mastered keeping the ROR on a steady decline tell us it avoids a baking defect, so the coffee is sweeter, juicier, and has less roasty flavors. There's been much less discussion on how to avoid an increased rate of rise before and into second crack. My roaster is different than yours, but to address the flick as beans become dryer and hotter, I increase airflow. Today I intentionally took a roast into second crack and even partly opening the bean charge chute didn't cool things enough to avoid a flick at around second crack.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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Almico
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#7: Post by Almico » Nov 10, 2019, 1:56 am

Controlling the RoR with air on a drum roaster is very difficult. Drum roasters pull air from under and around the drum into the bean mass. The air temp around the drum can vary greatly depending on flame and ambient conditions. sometimes turning up the air will pull in cooler air, sometimes hotter for a period. At a minimum you would need a probe where the air enters at the back of the drum to measure inlet temperature to make an attempt. I'm working on setting one up this week.

Better to control the RoR with heat settings. How far in advance these changes need to be made depends on the thermodynamic properties of the roaster. The rumor is gas makes fast changes compared to electric, but my roaster is gas with thick cast iron front and back plates, and all I can say is adjusting the heat is like steering the Titanic. It requires a lot of experience with roaster and bean, and a meticulously repeating process to get it right. Sometimes it works perfectly, sometimes not.

Here is a roast I just did tonight. The blueprint roast is in the background and you can see where the heat changes occur. When I made that blueprint I was using a constant air rate of 50%. Tonights roasts had the air at 25% until 3:35. You can see the MET bump where I increased air to 50%. Usually I reduce the flame about 30s before opening the damper to avoid too much of a BT spike. So yes, I need to make an updated blueprint.

The tricky part is the last heat adjustment before 1C. Rao has posted that changes to heat should not be made within 45s on either side of 1C. So that last adjustment at 1C - 45s determines the RoR trajectory for the next 1:30 during the most dynamic part of the roast! Different coffees react very differently at 1C and to maintain a steadily declining RoR requires more art than science. There are just too many variables for my limited cognitive powers. But if my roast hygiene was disciplined throughout the pre-roast and early roast process, the variation in outcomes shrinks dramatically.

You can see on the blueprint where the last heat change was made. For some reason the RoR on this roast plateaued just a bit at 1C, then dipped too much before recovering. I wouldn't call it a crash, but it's not ideal and that dip will show up in the cup. I like to take this coffee to 400*F at <18%, but the dip sent the RoR on a path that required carrying it longer to even get to 398*.

Image

This is why roasting darker and into 2C is so much harder than light roasts. You need to carry more heat throughout the roast to get to higher drop temperatures and still not allow a flick. If you can do it, you get unbearably sweet, chocolatey coffee with no raostiness* whatsoever.


* Freudian typo.
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drgary
Team HB

#8: Post by drgary » Nov 10, 2019, 2:50 am

Alan, thanks for the great post!

For beginning roasters be aware that temperatures and air settings on different roasters aren't comparable. You'll need to try suggestions like these and taste. What do you vary, then?

Here are a few things I'm learning as I go, other than those already mentioned, an incomplete list:

- Hotter or cooler charge
- Faster or slower overall
- More or less time spent in different stages (drying, ramp from drying to 1C, time in 1C, time after 1C, and if you go there, time in 2C
- Reading what others have done with this bean or ones of similar type and processing

Roasting is a deep rabbit hole!
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

Coffee Cougar

#9: Post by Coffee Cougar » Nov 10, 2019, 6:17 am

Thank you all for your quick and helpful replies. I am sorry for re-posting this question. I should have searched for an answer in topics similar to mine more thoroughly. On the other hand, I do agree with Peppersass; for me it felt like searching for a needle in a haystack (probably because I am simply unexperienced to both coffee roasting and using forums).
I will definitely give your suggestions a try on my future roasts.

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drgary
Team HB

#10: Post by drgary » Nov 10, 2019, 1:53 pm

I don't think an apology is needed for posting your question. As a beginning roaster, it is hard to know what to ask and to understand what you are seeing in a profile. There is so much information on this site that it is also hard to know where to search. After you have tried some of these suggestions, please post here to let us know your results.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!