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09/21/2021 8:53 AM
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Adventures in fluidbed roasting
allenb
So, after doing various experiments with controlling my small non-fluid, hot air roaster, via hot air temp, I want to share some results that I find very interesting and again is additional proof that conventional wisdom on what profiles are likely to give you best outcome are only suggestions and should never be hard fast rules for how you roast.

Example 1.
A Guat Huehue purchased in May this year has given me anywhere from ok to not so good outcomes in drum and fluidbed using various profiles that had always given me good results with many other coffees. I was ready to toss the greens into the trash until I did some additional roasts using the simple two stage approach I have been playing with for a few weeks. The stages were as before, 320F hot air inlet temp for 4 minutes and remainder of the roast at 510F. This resulted in the coffee ramping fairly quickly up to around 260F bean temp by minute 3 and basically staying at that temperature up to minute 4. The remainder of the roast at a hot air temp of 510 resulted in the bean temperature ramping very quickly to 400F where 1st crack started at minute 6:30 and ended roast at 7:35. Cupping results the next morning were excellent with nice balanced acidity, body and complexity. Probably the best quat I've cupped in years.

Example 2.
Uganda Bugisu purchased around the same time period was also getting close to being tossed due to not only having a "green" under developed taint but also with a pronounced woody note no matter how I roasted it using lots of variations of the classic curve. Using the aforementioned simple two stage approach, the coffee was remarkably better and very drinkable with much less earthy woody character and much improved complexity and body.

Another bit of info that proves that even slight variations can change a roast from ok to excellent.
In an attempt to see if what I accomplished above could be improved on, I made one small change by ramping the heat from 320F to 400F from minute 3 to minute 4 in order to prevent the coffee from stalling at 250F from minute 3 to minute 4. I was sure this would bring about an even better cup but was shocked to find it had degraded the cup and totally lost the body and complexity.

If someone had approached me earlier this year and told me they were getting great results with this method, I would have immediately written it off and would have been comfortable believing the person was unable to know what coffee is supposed to taste like and couldn't possibly be getting good results.

So, please never get comfortable with how you are now roasting and always be willing to try different roasting strategies. As many have stated, no one ever masters coffee roasting even though we get close from time to time. Of course, this is what keeps us drawn to the craft isn't it?
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
CK
Nice candid post Allen. I'm about five years into learning how to roast and have found that numbers, times, temperatures and curves do not always end in a great-tasting cup... especially on experimental machines. There are just too many variables involved with the process (from harvest to cup) to be stuck with one method of roasting. Like you, I've found that unconventional experimentation can bring great results too.
allenb
Hi CK. "Too many variables" yes indeed!

An outcome of my findings is I will now include taking any new green purchase through both the short hot air roast and a classic drum roast regimen to see if the bean favors one or the other and to also discover if I'm missing any flavor notes in either of them.

A Kenya Kigutha I picked up recently comes out really nice on both machines but displays very different sets of complex flavors using each method. Using the two roasters, it's almost like getting two different coffees from one purchase.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
CK
Roast Curves Screenshots; for a visual aid to see what happens with BT using this method of roasting

I've roasted two 600-gram batches, back to back, with a newly built hybrid roaster (drum/hot-air). First I used a generic stepped heater power profile, starting at 76% then stepped to 84% at 1 minute intervals. Second I tried the Schulman method you referred to in your post, with this machine at 50% power for 4 minutes then to 84% till the end of roast at 216C. It certainly looks off, but I'll cup them in a few days to see how greatly they differ, and just how good/bad they may taste.
CK attached the following images:
costa_rica_tarrazu_schulman_profile.jpg costa_rica_tarrazu_heater_power_profile.jpg

Edited by CK on 09/06/2021 7:23 PM
renatoa
Schulman advise about "ramp to...", not "step to"

Some 5-10-15% steps from 50 to 84 would made things look better, in the eye of a pixel
level graph peeper Grin
CharcoalRoaster
CK, do you have a build thread for your hybrid roaster?
CK

Quote

renatoa wrote:

Schulman advise about "ramp to...", not "step to"

Some 5-10-15% steps from 50 to 84 would made things look better, in the eye of a pixel
level graph peeper Grin


True, ideally stepping the heat would have looked better graphically and followed the recipe, but I didn't want a long roast, lagging 15-20 minutes.

How long should each percentage of ramp last from start to finish? I could program another batch to show a real-world graphic of what it would look like in that scenario... at least on this roaster.Grin
CK

Quote

CharcoalRoaster wrote:

CK, do you have a build thread for your hybrid roaster?


No, I didn't create a thread for this roaster.
renatoa

Quote

CK wrote:

Quote

renatoa wrote:

Schulman advise about "ramp to...", not "step to"

Some 5-10-15% steps from 50 to 84 would made things look better, in the eye of a pixel
level graph peeper Grin


True, ideally stepping the heat would have looked better graphically and followed the recipe, but I didn't want a long roast, lagging 15-20 minutes.

How long should each percentage of ramp last from start to finish? I could program another batch to show a real-world graphic of what it would look like in that scenario... at least on this roaster.Grin


Nope, not lagging anything, same levels, but at least an intermediate 70% step at 2:00, where RoC graph seems to start slowing its increase, should smooth a lot the drying phase of the graph, eliminating that RoC bump.
CharcoalRoaster

Quote

CK wrote:

Quote

CharcoalRoaster wrote:

CK, do you have a build thread for your hybrid roaster?


No, I didn't create a thread for this roaster.


Would you be willing to offer a short description and/or photos? I'm curious that's all... thanks!
allenb

Quote

renatoa wrote:

Schulman advise about "ramp to...", not "step to"

Some 5-10-15% steps from 50 to 84 would made things look better, in the eye of a pixel
level graph peeper Grin


So, it may be good for me to clarify what I meant by me saying I was using the suggestions by Jim Schulman.

As renatoa pointed out, Jims suggestion was to control ones roast via ET instead of BT since reading BT is unreliable and his preferred method was, as pointed out by renatoa, to step the temperature in ET or "ramp" it in order to more smoothly bring the beans up in temperature versus making abrupt, large increases.

The only reason I mentioned his method as relating to my experiments was in my using ET (hot air inlet temperature) for controlling my roast instead of BT. And, the only reason I've been sticking with a two step ramp instead of a multistep smoother approach is due to finding my coffee cupped better with the simple two step method.

If anyone wants to see if they get similar results as I have been getting, they will need to find ET temperature settings in two steps that allow the beans to be at somewhere between pale green and beginning of yellowing by end of minute 4 and to be at beginning of first crack by minute 7 or up to 7:30 and continue on for another 60 seconds hitting a light roast at completion. One should find a temperature for the second step that accomplishes this without having to adjust it between the beginning of 2nd step and end of roast. Depending on your hot air roaster's roasting dynamics (air flow, degree of agitation etc.) you may end up with widely differing hot air inlet temperatures to accomplish the profile in the time frame described.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
pisanoal
AllenB can you post up what one of these profiles looks like? I'm curious to try this myself.
CK
Curiously the profiles in post #4 cupped quite similarly. Always learning...

Here's another concept from Nestle. They roast the first part of the process, and then when you're ready you finish the roasting on your machine. See paragraph 2 under the video on this page...

https://www.nestl...ut-of-home
renatoa
This is indeed a mind blowing approach... Shock demolishes all we think we knew about the roasting process...
allenb

Quote

pisanoal wrote:

AllenB can you post up what one of these profiles looks like? I'm curious to try this myself.


I'm not charting my roasts but the next roast I do, I'll jot down the bean temps at 30 sec intervals and I'll report back.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
allenb

Quote

allenb wrote:

Quote

pisanoal wrote:

AllenB can you post up what one of these profiles looks like? I'm curious to try this myself.


I'm not charting my roasts but the next roast I do, I'll jot down the bean temps at 30 sec intervals and I'll report back.


Ok, here's the bean temperature time/temps for the two step hot air roast with hot air setpoint of 320F for 4 min and then 510f for the remainder. Realize that your roaster's thermodynamics might require a totally different pair of temperatures to get in the neighborhood of the profile. And, as you can see, it's an odd profile with absolutely no elegance. Also, one can really see the naturally occurring declining RoR when using fixed temps instead of ramping. I don't think there is any accuracy in my bean temps during first crack and up to end of roast but that is what the thermocouple is reporting. One can see the huge affect that the vapor release causes during 1C in trying to read the beans.

30 157F 69.44C
1:00 197F 91.66C
1:30 213F 100.55C
2:00 224F 106.66C
2:30 240F 115.55C
3:00 245F 118.33C
3:30 250F 121.11C
4:00 252F 122.22C
4:30 300F 148.88C
5:00 339F 170.55C
5:30 364F 184.44C
6:00 381F 193.88C
6:30 397F 202.77C
6:42 400F 204.44C first crack start
7:00 403F 206.11C
7:30 407F 208.33C
7:42 412F 211.11C end (first crack slowing down)
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
renatoa
A suggestive graphic representation of "huge affect" of the FC on hot air evolution.
Roast is done a hot air machine, not a FB, but the shape apply to FB also.

Beware, if temperatures range isn't a good hint: the data plotted is of air, not beans.
...
renatoa attached the following image:
0510_eth_yirgacheffe_gr_1_cherry_red.png
renatoa
Regarding ramp vs step debate, and the "how many steps" question, is hard to find an answer to this by trial end error instead performing a step response test of your process.
https://en.wikipe...p_response
Having such test done, it's easier to simulate a ramp composed from several small steps, as in the attached image.
...
renatoa attached the following image:
3dfeb315ff28c7e1c4117f6bf283836bede474dd.jpg
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