Drying phase ramp up - Page 4

by **another_jim** on Wed Jun 24, 2009 10:56 pm

There's a bit of luck here: the moisture content of fresh coffee should be between 9% and 13%, and this is where the graph shows the greatest changes in RH for moisture content.

So I think an RH meter may yield a simple decision rule: Use your standard drying profile between 60 and 75, shorten it if the humidity is lower, lengthen it if it's higher.

by **Coffeengineer** on Thu Jun 25, 2009 7:17 pm

Jim I think the number might be a little lower, here is a doc that looks like it was copied from somewhere else that has a sorption isotherm for parchment arabica at 25C... (taken from Stirling's Kenya Coffee, 1974). What was a bit more concerning was the plot of degradation in cupping quality vs moisture content. How can one maintain cupping objectivity over 12 months?

Here is a reference that states ERH and aw (water activity) are numerically the same. Also shows that isotherms move to the right as temp increases (barley @ 20 & 30C).

I find high quality recent shipments cluster around 61% (59-63) with some outliers possibly representing problems in the supply chain. Water decaf is different, giving a higher reading probably due to the processing. Perhaps you could run through your collection and compare with your roasting notes and summarise.

The RH meter I am using is just a cheapie from fleabay that i picked up on spec to test the theory, not having any absolute numbers to relate to. Looks like it is worth using at least as incoming QA, and also for drying hints. My experience is that over drying is usually more of a problem than under (= flat coffee and extended rest times).

Eric

by **GregLee** on Thu Jun 25, 2009 10:10 pm

Fullsack wrote:The other problem created by the high ET charge and fast drying phase ramp was bean color often seemed to go from a greenish yellow to a light brown without ever hitting bright yellow.

I'm just starting roasting with a Toastmaster popper, no thermometer, and I don't generally see bright yellow beans. Looking at the following suggestion for the drying phase from another_jim:

another_jim wrote:Here's how to get some very basic profiling on a completely unmodified popcorn popper:

Drying phase: Run the roaster one minute, then turn it off for two minutes, then restart the roast. Increase or decrease the turnoff time to change your drying time.

I ran my popper for a minute on 100g of beans (Supremo) and turned off the popper, continuing to stir the beans with a wooden spoon for two minutes. I saw some yellowish tint, but no real yellow, so I turned on the popper for 30 seconds then off for a minute and 30 seconds, stirring, and saw some yellow, but not very bright. Another 30 seconds on and then 30 seconds off made the beans even yellower.

Am I on the right track do you think? It took me 6 minutes to get yellow beans -- is that too long for the drying phase?

by **another_jim** on Thu Jun 25, 2009 11:16 pm

Buy a thermocouple thermometer, they only costaround $10 to $20.

Mount the TC so it's just above the bean mass at the end of the roast. Run the roaster so it gets to 300F. Turn it off a few minutes, take break, don't stir. Restart the roast. Some of the beans should start going yellowish when you reach 300F the second time, and most should have lost their green color. Don't go for completely yellow.

by **Ken Fox** on Fri Jun 26, 2009 2:03 am

Coffeengineer wrote:I have a suggestion that I am trying with some apparent success: when a greens shipment arrives i drop one of those RH/temp panel meters into the beans and seal them up in my 16C constant temp wine cellar. After 1-2 days stabilisation of temps & RH the meter reading for relative humidity gives a rough guide to moisture content - enough to adjust phase 1?
Eric

Who cares? Put the beans next to your bottles of Grange Hermitage, and after a month let us know if you note any improvement.

ken

by **timo888** on Fri Jun 26, 2009 7:24 am

Forgive my naivete as an armchair roaster, but why would one be content with rough-and-ready bean dryness metrics established before they're roasted? Why wouldn't one be measuring instead the moisture inside the roaster itself with a high-temperature thermo hygrometer?

by **GregLee** on Fri Jun 26, 2009 11:27 am

another_jim wrote:Buy a thermocouple thermometer, they only costaround $10 to $20.

Thanks and I'll try that. The particular device you referred to would have cost $35 with shipping to Hawaii, so I ordered this for $12 (which perhaps displays only centigrade). Hope it works.

by **GregLee** on Fri Jun 26, 2009 4:40 pm

another_jim wrote:Mount the TC so it's just above the bean mass at the end of the roast. Run the roaster so it gets to 300F. Turn it off a few minutes, take break, don't stir. Restart the roast. Some of the beans should start going yellowish when you reach 300F the second time, and most should have lost their green color. Don't go for completely yellow.

My first try at this didn't work to produce any yellow beans. It took 2:15 to get up to 300F, by which time the beans were already slightly tan without having gone through any yellow phase. After an off period until elapsed time was 5:00, I continued up to 300F again, seeing only more tan. (First crack came at 388F, second crack at 10:30 elapsed time, and I continued to 12:00 to get a Vienna roast. Batch size 100g green, 83g roasted. Guatemala SHB EP Estate Antigua "Los Volcanes".)

by **another_jim** on Fri Jun 26, 2009 6:40 pm

Hi Greg

I'm not sure why you are going doing this for a Vienna roast. Does the roast taste grassy or chlorinated? The trick of turning off the roaster is aimed at removing grassiness from lighter roasts.

On color: The beans start out green, They go yellow to light tan in the low 300s, (I'm not talking saturation, just tint and value), and an even tan color in the mid 300s. Then they get uneven during the first crack, but should come out of it an even brown color. For a roast stopped before the second crack starts, or just at the very first pops, it is best that the drying phase is arranged so the beans go through this color progression at the stated temperatures.

The problem for Vienna roasts is usually ashiness. For these darker roasts, unregulated air roasters do quite well without any special tweaks, since carrying excess moisture into the first crack can reduce ashiness. For such roasts, don't do any stalling; and let the beans go throught their color progression about 30F higher than stated. If the roasts now taste ashy, reduce your load, so that the air temperature blowing in stays a little lower.; if the roasts are too slow finishing, increase your load to raise the supply air temperature (by slowing down the airspeed).

Most of the people posting on profiles are roasting light. If they don't talk about roast depth, they are usually dealing with the tasting issues one encounters in City and occasional Full City roasts.

by **GregLee** on Fri Jun 26, 2009 7:30 pm

another_jim wrote:I'm not sure why you are going doing this for a Vienna roast. Does the roast taste grassy or chlorinated?

No, it's just not tasting that great. It's not obnoxious, but it's not very interesting. I'm casting around looking for improvements. Are you saying here that dark roasts don't profit from a controlled drying period? Or that someone who likes dark roasts may as well not bother trying to improve.


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