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The best charge temp is the highest temp you can achieve without any scorching/tipping
yes yes 50%[1 Vote]
no no 50%[1 Vote]
Total Votes : 2
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Finding first principles - charge temp
Moliin
Introduction

Hi everyone!

I hope this is the right place for this kind of post. Otherwise I will be happy to move it somewhere else.

First, let me introduce myself. My name is Kasper. I am born in Denmark, but have spent the last 10 years in the Netherlands studying music and working as a cook.
I am obsessed with coffee. When I was still living with my parents they invested in an espresso machine and since we lived away from major cities a Gene Cafe soon followed. Since then I have gone deeper down the rabbit hole of coffee brewing reading everything I could get my hands on while trying some of the best coffees from around the world. But I never really got into the finer details of coffee roasting.

However, I have gotten my hands on my very own Gene. A friend of mine didn't need it, so he figured I might as well put it to good use. So this is my chance to learn more about roasting.

First principles
So here's my plan: I want to go through all the stages of coffee roasting learning the basics along the way.
I have read a lot online from which I have learned a lot. But mainly I have learned that there's a lot of conflicting knowledge out there. Some might be dated, some might be incorrect, some might just be imprecise.
So I want to boil everything down to first principles. Make myself some rules that I can build my technique and theories upon. And along the way I want to document what I find, what I wonder and hopefully get input from people who know more than I do (this is not a particularly hard bar to clear).

First first principle: Charge temp
I propose this: The best charge temp is the highest temp you can achieve without any scorching/tipping.

I am not sure exactly what I am making this assumption based on, but so far that seems to be what my accumulated reading has suggested.

Roast batch 1 - Nilza

Origin: Brasilien, Espirito Santo
Farmer: Nilza, Montanhas Santo
Variety: Red Catimor
Process: Natural

I generally like my coffee lightly roasted (I am Scandinavian after all) but this particular coffee I have tried light and didn't really think it did it much good. So I am going for a medium roast.
This is how I went about it:

(roaster is an unmodded Gene Cafe)
Charge temp: 200c (preheated gene for 100 minutes at 200c)
Initial roast temp: 240c for 11 minutes
After 11 minutes: 225 c for 3 minutes
Cooling: Colander and fan

Things I have learned:
Colander and fan cooling should be done out the window if you want to avoid getting chaff everywhere.
Forum posts, however interesting, should not be read during roasting if you want to keep track of what you are doing.
200c might be just too high for this setup. Beans look okay but some show a bit of tipping. Will lower next batch to 180.

Picture of the roast:
https://photos.app.goo.gl/njAf7cbsA8S...sA8S4jH1o9

Picture of beans showing light tipping:
www.bit.ly/2DM2rUV

I hope some of you will join me and help me learn more about roasting. I will keep posting as I roast more batches and try to focus on different aspects once I feel more confident in my charge temp. Now I will go clean up a living room full of chaff.
Edited by Moliin on 09/22/2020 12:06 PM
renatoa
Welcome ! Welcome BBQ grill

Quote

Moliin wrote:

I have read a lot online from which I have learned a lot. But mainly I have learned that there's a lot of conflicting knowledge out there. Some might be dated, some might be incorrect, some might just be imprecise.


You have no idea how true is this when related to Gene... Grin
I didn't found this until I opened one for TC4 modding.


Quote

Moliin wrote:

First first principle: Charge temp
I propose this: The best charge temp is the highest temp you can achieve without any scorching/tipping.

I am not sure exactly what I am making this assumption based on, but so far that seems to be what my accumulated reading has suggested.


Apparently this could be true, but not apply for Gene because immediately you press start the beans are flooded with hot air in excess of 300C degrees, much more than the preheat temperature.
Here is a first point where Gene do it wrong: this intake hot air temperature is not regulated in any way, and heavily dependent on mains voltage.
There is only an emergency sensor, that cut heater at all, in case of a very high temperature, perhaps to prevent fire.
So please measure your mains, and if you are significantly over the standard 230V, then your hot air temperature needs a check. On my 238 V mains I found 330 C degrees, much more than the 270 C limit where the beans structure start destroy, cellulose melts.
Fortunatelly, such small difference can be easily fixed, for example placing a 55W 12V H3 car bulb in series with the mains line. This bulb current match closely the Gene current when heater on, about 4-5 Amps, so the mains voltage will be reduced by 10-12V.
For 110V mains the solution should be different... double current, less voltage...

Quote

Moliin wrote:
...
(roaster is an unmodded Gene Cafe)
Charge temp: 200c (preheated gene for 100 minutes at 200c)
Initial roast temp: 240c for 11 minutes
After 11 minutes: 225 c for 3 minutes
Cooling: Colander and fan

Things I have learned:
Colander and fan cooling should be done out the window if you want to avoid getting chaff everywhere.
Forum posts, however interesting, should not be read during roasting if you want to keep track of what you are doing.
200c might be just too high for this setup. Beans look okay but some show a bit of tipping. Will lower next batch to 180.



Too much preheat time, imo... there is no reason to keep it that long.
You should be aware how to read the temperature display of Gene:
- the value means the exit air temperature, not beans.
- when the preset value is reach, the heater start to on-off 100% pulse, resulting in a variation of hot air temperature in the 200-300 C range, the goal being to maintain the preset exhaust temperature.
- waiting longer after this "stable" temperature regime was been achieved will not result in heat accumulation, as for an espresso machine, or other benefit.
- so you can load imediatelly after preheat preset, no wait needed.

The temperature profile used don't look right to me, but you give us no clue about the temperature variation during the first 11 minutes.
Well, you set 240C as a target, how fast was it been achieved ?
Actually, the 11 minutes time tell me that it was never been achieved, maybe low voltage mains, or your Gene has a measurement issue.
Why I say this... because a right loaded machine, when beans are immersed in 240C hot air, should have first crack in the 8-10 minutes ballpark.
Low voltage mains is a guess that worth verifying, I know a case where Gene powered from 190 V mains, and set to 245C, was never been able to reach it on display. Nor having a healthy FC.

The second temperature step, at 245 C, is too much step down of temperature, if the intended reason is to compensate first crack heat release.
Actually, a well tempered process does not require lowering final temperature at all, but let the natural curve do its job for you.
What I mean by this riddle... Grin
If you go at this address: https://www.symbolab.com/graphing-cal...calculator, and input this equation: 25 + 220 * (1-exp(-0.003 * t)) in the upper left text panel...
... you will see drawing the most perfect profile you can dream to achieve.
The 200 C line, where is the typical FC, will be crossed at 8:30 (510 seconds), and from there the profile will continue with a nice 6 C / minute increase rate.
What is this equation about? Nothing else than physics... thermodynamic law of a body heat absorption when immersed in a hot environment.
How should we read the parameters: 25 is the ambiant, 220 is the environment temperature delta over ambient, thus ET = 245 C (ET = environment temperature), t is time, and 0.003 is a constant embedding all the physical characteristics of the process: machine, beans, moisture, everything.
The fact that you have FC at 11 minutes, much later than the 8-10 minutes ideal range, related with the curve above, tell me that your machine internally could never achieve the 240 C degrees you preset. That's why is important what is the temperature evolution on display.

Next point... Lowering the ET at first crack so dramatically, to 225 from 240, will led to a serious fracture in this perfect profile, and led to baking the roast, no wonder you don't like tasting it.
So, instead lowering temperature at the end of roast, is better to try finding the optimal ET temperature that led to a natural developed profile without any temperature change during the second half. Or very small tweaking, I am talking about 2-3 degree maximum.

Additional on this subject you can read here: https://forum.homeroasters.org/forum/...ad_id=5300

This info you will find in the thread first post, related to the physics law behind the curve drawn above, are all you need to know to adjust your roast for better.

And the last... Why do you thing lowering beans will reduce tipping ?
This is caused by too much hot air too early on in the roast. The bean cannot absorb heat fast enough and so cannot transfer the heat throughout the bean.
So a better idea would be to reduce preheat temperature instead, and start roast temperature, according to the lecture of thread above.
Moliin
What a wonderful reply! A lot to take in though. I will cut up your reply a bit to try and keep an overview.

Quote

Welcome !

Thanks!

Quote

And the last... Why do you thing lowering beans will reduce tipping ?
This is caused by too much hot air too early on in the roast. The bean cannot absorb heat fast enough and so cannot transfer the heat throughout the bean.
So a better idea would be to reduce preheat temperature instead, and start roast temperature, according to the lecture of thread above.

Just wanted to get that out of the way first. I wasn't very clear in my post but I did indeed refer to lowering charge temp.

Quote

Apparently this could be true, but not apply for Gene because immediately you press start the beans are flooded with hot air in excess of 300C degrees, much more than the preheat temperature.

Do I understand it correctly that you are saying that it doesn't apply to hot air roasters but only to drum roasters? And by extension that preheating doesn't really make much of a difference in a gene since most of the heat transfer in convection and not conduction?

Quote

So please measure your mains, and if you are significantly over the standard 230V, then your hot air temperature needs a check.

Will do! Now to figure out how.

Quote

Too much preheat time, imo... there is no reason to keep it that long.


The reason I did it this long is to be absolutely sure that all of the drum is completely heated to make the process more repeatable. Is that not of importance?

Quote

The temperature profile used don't look right to me, but you give us no clue about the temperature variation during the first 11 minutes.


So this is where it gets embarrassing. I got so caught up reading about charge temp I walked away from the roaster while happening so tbh I don't have much of a clue myself. I will take better notes for my next roasts.
But I must also confess that I am having trouble hearing it through the noise, so I might have also just noted it at the wrong time. I live right above a busy street so I might have better luck practising going by sight.

Quote

Next point... Lowering the ET at first crack so dramatically, to 225 from 240, will led to a serious fracture in this perfect profile, and led to baking the roast, no wonder you don't like tasting it.
So, instead lowering temperature at the end of roast, is better to try finding the optimal ET temperature that led to a natural developed profile without any temperature change during the second half. Or very small tweaking, I am talking about 2-3 degree maximum.


This is a great point. Finding a set ET temp would have the added benefit of making my roasts easier to replicate as there would be one variable less.


I will take a look at the link you posted. Thanks a lot for your response. Very helpful!
Moliin
So a few roasts later I am slowly getting some results to look at.

All my roasts have had an unpleasant roastiness. Lowering charge temp to 180 has helped but not removed it. At 180c I still get a bit of tipping. My roasts are now pleasant as espresso but too roasty for filter. Yesterday, I lowered my charge temp to 160 which visually seems to have solved the problem. It does however add around half a minute to my roast.

I have yet to cup the newest roast with the charge temp at 160 so I am hoping it will remove it.


Here is the log from my last roast.

Bean: Nilza Brazil (natural)
Preheat: 5 min 160c
Setting: 245c
Temp after 5 min cool: 24c
Weight Loss: 13,25%
FC: 10:52
End: 11:45

Time:temp
01:174
02:196 (I was a bit late noting this so it might have been lower)
03:204
04:212
05:219
06:225
07:231
08:236
09:240
10:242
11:242


It was dark out and I got quite some smoke so I chickened out and ended the roast earlier then my planned development time of 1:30.

My new way of cooling is to dump the batch into a GN1/1 tray and cooling with a fan. It works much better than a colander. My best result with a colander and fan was 42c after 5 minutes.
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