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"Well tempered roaster" more feedback
Is not controlled by PC, but a TC4 on st-ESP-roids Grin
This way there is no more need for computer, the extensions added to original TC4 software give me all the info I need to get rid of Artisan.
Hi all,

Inspired by allenb's and renatoa's comments I gave the two step process a go. After some trial and error I was able to achieve the following roast using a peru wet processed bean from sweet maria's. This seems to be in line with several of the suggestions of dry end about 4 min, then 3+ min to first crack and then shutting off just after first crack (one or two pops still going on). I have not tasted this yet, but how does this look?
alnt attached the following image:
The most important interval in your graph, after minute 5, looks very well ! Drying is not so critical. Well done !

First step should be around minute 2.
The sign who show us is the flattening of ET under 200 C / 400 F, first checkpoint after load is to reach ET 200 C within 1-2 minutes.
An Ikawa lecturer recommends even 218C / 424F as target of ET through dry phase.

Next hint is the corresponding RoR drop due to ET flattening.
Is optimal try keeping RoR average around 40F/20C during dry phase.
I would increase power immediately when I see Ror dropping under 50 and heading to 40, in your graph.

Two steps is not a mantra. You can try three, even four smaller steps, if you are able to achieve a smoother RoR decline.
Edited by renatoa on 11/22/2021 6:48 AM
Thanks for the tips. Iím traveling over the holiday so I wonít be able to try them out for a while, but Iíll post results when I have them.
I brewed the coffee from the profile shown above in an immersion cone after the coffee sat for about 1 week in a sealed jar, and it had more acidity and sweetness than previous roasts of this coffee. I don't have a refined enough pallet to pick out fruit flavors (if there are any), but I did notice a hint of tea-like flavor as the coffee cooled.

When I roast again I'll try renatoa's hints and see what impact those have. It's getting relatively cold here, so my batch size will probably shrink from ~150g to 130g to give the same level of control over the roast - more opportunities for experimentation!
Cold will have greater impact on roast than the profile subtleties will debate here.
Mains voltage variations also.
I roast outside only when above 22C and no wind, else indoor.
Attached is a plot of roast ruined by wind gusts Grin
renatoa attached the following image:
Ouch! It should not get that extreme for me. I roast indoors in my garage, so no wind to deal with. The ambient temp has been in the range of 15-20C over the past couple months, but now it will be more like 5-10C.

I have been considering how to upgrade my roaster to recycle hot air from the exhaust to help a bit, but it hasn't been a priority yet. We'll see what this winter brings....


renatoa wrote:

The 200 C line, where is the typical FC, will be crossed at 8:50 (530 seconds), and from there the profile will continue with a nice 7 C / minute increase rate.
The equation above is the one from the theory post, thermodynamic law of a body heat absorption when immersed in a hot environment.
How should we read the parameters: 25 (C) is the ambient, 245 (C) is the hot air temperature, the infamous ET Grin, t is time, and 0.003 = k, is a constant embedding all the physical characteristics of the process: machine, beans, moisture, everything.

Is there a simple equation to adjust ROR post FC based on ET? Going with a 90 second dev time, but I would like to adjust the ROR to end around the same roast level to replicate this experiment.

I am trying to find a way to calculate temp drop post FC to reach the right dev time without overshooting my final temps. I am very close to on par with the "perfect" roast curve with an 8:15 FC, but going 90 seconds into DEV time would put me at 210.5 C much to hot to be a "light roast" and if I then attempt the next step at 143 seconds DEV time I will be nearly at a Dark Roast.

If I understand everything correctly there is no "inertia" with a FB roaster (or limited to the time it takes to drop ET), so I can't adjust my roast curve leading up to FC otherwise I will just push FC out further. I need to keep the ET on point to hit FC at the time I want and then adjust ET to extend my roast and drop my ROR to the correct amount for the desired DEV time and roast level. (light to medium light).

I would basically need to adjust my temp post FC to get half the ROR to hit my 90S dev time. That obviously wouldn't be half the temp, not sure if it would be half of the difference or how that equation would work out. Any help here to save a bunch of trial and error would be nice.

Of course I could push more temp earlier to get so I can drop ET prior to FC, but that appears to be bad as it would scorch my beans and give me production quality coffee.


Is there a simple equation to adjust ROR ...

No, because post FC the beans themselves becomes heat source, and cooling factor, in very fast sequence.
The equation discussed so far is valid only for the heat absorbing section of the roast, i.e. about 5-10 degrees before FC.

For my roast in hot air machines, but not FB, I try to adjust power in the dev stage to have 7-8 C degrees increase in about 90 seconds window.
This is for what I call medium roast, 14% weight loss.
I do this monitoring exclusively RoR, no BT, no ET... and playing with power just 1% at a time.
Goal is to enter into FC with Ror around 7, and don't let it drop below 4.
If FC happens above RoR 7, would lower power by 1%
When RoR drop below 5, raise power by 1%, and again if the drop continue below 4.
When RoR recovers above 4, lower power by 1%, and watch to keep it in the 5 C/min ballpark.
When RoR sky rocket above 6-7, the FC is done, and be prepared for drop, if the dev time is ok for you.

Put these in an equation Grin

PS: all rates are in Celsius degrees, per minute


renatoa wrote:


Is there a simple equation to adjust ROR ...

No, because post FC the beans themselves becomes heat source, and cooling factor, in very fast sequence.
The equation discussed so far is valid only for the heat absorbing section of the roast, i.e. about 5-10 degrees before FC.

I am a little confused on this concept. The Beans would not be a heat source, they would just be storage for heat. If you cut out the heat energy to them they would cool. But assuming they are at 200 C for first crack, there has to be an equation to calculate the heat energy (assuming uniform application like an FB) required to continue to raise the beans at a desired rate.

There could be some cooling complications from FC moisture release, but that would be very limited in an FB where that moisture would be quickly expelled in the air.
That's the point... it's true what you say, but only up to a point... when beans reach a certain internal temperature that starts an internal combustion, is what we call an exothermic reaction.
This means they become a source of heat, for very short period though, because this internal heat led to increased pressure of the steam accumulated inside bean, and we have the crack, the audible outcome of this process.
On the roasting graph this can be easily recognized as a bump, that was called "the flick" in the roasting industry.
The steam released through the crack, because losing pressure, will led to a cooling of the environment around the bean, it's the "crash" after the flick.

For an unknown reason to me, someone launched the mantra that this is a bad thing, and from there people fight with various heat management maneuvers to minimize this effect, i.e. make the passing through FC as smooth as possible, on the graph.
And here we arrive to what you proposed... reduce heat before FC... even with the risk of losing the audible part of the crack ?! Shock ... that become a fizzle instead a crack ?...
Then complain that you don't hear it... d'oh... Grin
Like close the mouth of the beans... d'oh... the censorship exist in beans world too... Grin
It sounds like the solution is to sacrifice more beans to my clover to see if this hearsay has merit.
I wanna know! Sacrifice some beans for the cause. We're all counting on you to deliver the truth! Seriously!
Clever Coffee Dripper
Grinder: Macap M4
Roaster: Completed drum roaster project photos shown here:
Videos https://www.youtu...Bd1NrdpSUH
Sacrificing some beans will produce a conclusion valid mostly for a machine class.

To reply first to @exer31337, you should do nothing during development, because you are right, the high airflow will make pass the FC cooling unnoticed, at least so was in my experiments with two different machines, a SR chinese clone and also on an asymmetric design.
In both cases all I had to do is to push 1% more power after FC top (the flick), when the crash looks starting. I can post graphics to illustrate these cases.

However, for other machines, where airflow is lower, keeping on track requires my full attention, and even 3-4 changes during development.

For drum roasting is a matter of knowing the machine, plan and execute.
No idea if something can be changed once the development is already rolling... and derailed.
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