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What do you do after FC Keep power where it was increase or decrease?

I don't know how many times I have to link to this. It's a dissertation on coffee roasting. One part of the dissertation is on roast profiles, and deals with the profiles used by the major instititutional roasters (mostly Nestle's, since they paid the Schenker's fellowship).

They have a simple three step profile for ET:
1. they blow the air in at around 350F for two to four minutes,
2. raise it to 475F or so over the next two to four minutes,
3. and leave it there to the end of the roast.

renatoa wrote:

Almost all was been already said here: https://homeroast...post_62977

The FB specifics are handled starting with post #43, second page, but it worth reading from the start, imo.

allenb wrote:

Quote from Jim Schulmans thread at Homebarista linked to by renatoa above:



After again reading his important posts on this subject, it occurred to me that this is exactly what I've settled on for the best results in my Freshroast 70 gram fluidbed.

ET starts at 352 F (177C) and holds for 2 minutes, my Fuji ramp/soak controller then takes it on a 3 minute ramp to 478F (248C) where it holds until end of roast and allows the development stage BT to cruise at close to 7-8 degrees F per minute plus or minus a degree.

This allows a 7 to 7 1/2 minute light roast finish. But, while this works in my Freshrosat with it's fully perforated flat bottom RC, these ET temps are not hot enough to give the same results in a standard conical or asymmetrical bottomed fluidbed. The temps would need to be more like 400F (204C) for first phase and ramp up to 500F (260C) for final end of ramp temp.

exer31337 wrote:



Not the answer I was hoping for but thank you for the honesty. I was using that as a generic guide, but I feel like my roaster goes a little to fast at times.

I've checked ET with an infrared thermometer, an oven analog thermometer (which was accurate in the oven), and now 2 different digital thermometers. I keep getting max temps of about 350F but I keep hitting FC in about 7-8 minutes with 350 Deg ET...

When I went off that guide I was hitting FC in 5-6 minutes and getting a little under roasted.

Don't know if anyone else has had the problem with a pure FB roaster.

...This ET part is basic roasting chemistry, and the same for all roasters and coffees.
But the heat inputs required moment by moment to achieve this ET curve is based on the roaster's thermal characteristics, and is different for every roaster design.

renatoa wrote:



Which way I was dishonest in my reply ? :puzzled:

If you mean that your initial question, as well the term used in the title, are related to power control profile, not ET, then apologies if I wasn't clear enough, will state here again, maybe a bit reworded: in the hot air based machines of small capacity and low inertia, as are FB, the ET is proportional with power % to such degree that they can be used interchangeable.
Based on this rule I developed the "proportional on setpoint" approach of power control, about you can read more in post #45 of the thread linked above.
The three steps rule of Schulman is nothing else than an over simplification of the same reasoning.
Instead using 20-30 steps of 1% every 10-20 seconds, he steps only two times with bigger steps, and it works very well, due to the thermal inertia of the bigger machines he is using.

Not the last, quoting again a key phrase from his lectures:

...i.e. what works for me is not mandatory to work for you equally better

allenb wrote:

It’s unfortunate that there are some greens, in my experience maybe 1 in 10, that due to whatever processing issue’s occurred, will not be happy with anything under a 10 min roast. For example, one of the better rated Kenyas I purchased last week had a green, underdeveloped taint with a 7:45 finish. Some of these with processing problems won't be any better with a longer roast.

If that is happening to most of your roasts then there may be other issues. Can you post the BT curve for a typical 7 min roast?

renatoa wrote:

Where the profiles comes?
Much simpler then most people thinks... from physics/thermodynamics.
If you drop a body in a hot environment, that body absorbs heat and increase its own temperature according to this law:



where: AT is ambient, k is the machine constant, and t is time

If you plot this equation, for example for ET = 230C and k = 0.0032, as I found for my TO based machine, you get the following, attached image.
This shape is probably a perfect profile for many of us, with 150C for Dry End reached at 240 seconds = 4 minutes, and 200C for FC reach at 450 seconds = 7:30
What we are doing in real life by changing ET means actually change the dry and brown intervals according to same law, and according to machine and bean origin specifics.

That's why Schulman recipe for the basic roast is so simple, all you have to do is to keep beans in a hot (stable) environment, and keep them moving. A power level for dry, and the second/next for brown/development.
Posting exact values of ET or power... would not help so much, my machine is different than yours.

exer31337 wrote:
...

I've checked ET with an infrared thermometer, an oven analog thermometer (which was accurate in the oven), and now 2 different digital thermometers. I keep getting max temps of about 350F but I keep hitting FC in about 7-8 minutes with 350 Deg ET...

When I went off that guide I was hitting FC in 5-6 minutes and getting a little under roasted.

Don't know if anyone else has had the problem with a pure FB roaster.

If FC starts at 398f ...

renatoa wrote:

Exactly... even 5 degrees off could be a matter of calibration, not reading error.
For air the best is to place a naked junction inside a pipe with holes like a flute, this is the industrial standard for gas measurements.
Some examples:
https://www.tegam...-t-airgas/
https://de.farnel...dp/7081625
For DIY, even a spring could replace the pipe, as this:
https://www.amazo...B007JN08KI

Somewhere between my lines above I suggested this is one of the main reasons I am thinking in terms of power% instead temperatures... I trust them more :)
Or Watts, measured directly at mains plug, a domestic wattmeter is cheap today...

renatoa wrote:

Somewhere between my lines above I suggested this is one of the main reasons I am thinking in terms of power% instead temperatures... I trust them more :)
Or Watts, measured directly at mains plug, a domestic wattmeter is cheap today...