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Topic: new time/temp curve? (long) (3 msgs / 121 lines)
1) From: Simpson
 
Over the past several years in this group we've kicked around time/temp 
curves for roasting and the two basic ideas I've gleaned from this and 
other groups (alt.coffee) were 1) ‘slam’ the beans at high temp through 
until they are roasted and 2) dry the beans at a low temp then gradually 
ramp up the temp until the desired roast is reached.
Recently though, Jim of Black Bear and Ian Bersten just tonight on 
alt.coffee, discussed a temp profile where the green beans are exposed to 
initial high temps while they are moist and can stand this treatment and 
then the temp is lowered until the roast essentially coasts home the last 
few degrees. Here’s a brief quote from Ian’s alt.coffee post:
“I have today started using a Brambati KS120 roaster…”
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“The roaster heating profile is designed to mimic the normal roasting 
practice of high heat for the first few minutes and then a gentle heat 
until the end - it cuts the heat off at a predetermined bean temp/time -the 
beans always reach a given temperature at a given time and then you can let 
the final four to eight degrees be attained without extra heat from the 
roaster…”
When I read Jim’s discussion several weeks ago I started thinking of how to 
reach higher initial temps so as to match this described curve. My problem 
has been that, with my fluid bed electrically heated roaster, temperature 
has been a function of air velocity. The more air that travels over the 
coils the cooler the resulting roasting air is… the less air that travels 
over the coils the warmer the roasting air is. So early in the roast when 
the beans are at their most dense I usually have to have more air just to 
loft them and this meant lower temps. Perforce I've been a proponent of the 
“dry at low temps, and raise temps as the beans are lighter and the roast 
progresses’ school. This was because I could lower the air velocity as the 
beans grew lighter and this meant higher temps. Less air, higher temps, right?
Tonight I added another coil to the VR MK5 which is now the VR MK6. I can 
move about a pound of beans and reach temps of about 475 to 500 degrees F 
even at first when the beans are dense. I tried a roast of 3:1 Malabar Gold 
to Harrar ( both from Tom’s Little Shop of Harrars) tonight where I heated 
the green beans aggressively as Ian and Jim describe and then cut off the 
aux coil and  was able to keep decreasing heat with the roast progressing 
nicely anyway until at about 11 minutes it reached active second crack 
(this is an espresso blend) and the bean temp (surface, indicated) and the 
air temp were almost the same. Cool! Usually there’s at least a 40 degree 
difference or the roast doesn't progress.
Using the old method my beans (same blend and roast degree) looked a trifle 
scorched and dry… more a dark black/ brown than a mellow dark brown. They 
almost looked sooty. Tasted good and had a nice aroma but they weren't as 
pretty as some pro roasts I've had. Tonight’s roast is a lovely dark brown… 
same roast degree as before, measured by degree of activity into second 
crack as well as indicated bean surface temp, but the color is much nicer 
on tonight’s roast. I'll pull some shots on Sunday and let you know how 
this stacks up. They are as lovely as any pro roast I've ever seen.
This initial high temp and then cooler temps until the roast coasts to 
completion makes a lot of sense to me. I don't *think* its possible to 
emulate this easily with the usual fluid bed tech (i.e., corn poppers) but 
the stove top and modded alp folks should be able to do this since temp is 
not a function of airflow with them. If anyone tries this let us know how 
it works. This almost seems like the classic stovetop profile of an initial 
high temp which the beans cause to cool down and which then slowly roasts 
the coffee at a more steady temp than with the ‘slam-thru’ or ‘dry then 
roast’ profiles the fluid bed folks seem to be stuck with… Maybe that’s why 
the stovetop roasters are described as producing more body and a more 
complex roast?
Later-
Ted

2) From: Mark Beckman
I enjoyed your post Ted, got me thinking about the roasting temperature
profiles.  Unfortunately, I've got more questions then answers at this
point.
With my drum roaster, which has two 600 watt heaters, I do not have as much
control as you seem to have.  I can set a "target" temperature (bean
temperature) and when the termperature is reached, the heaters turn off.
Then, the bean temperature will rise up to 10 degrees, similar like the post
in alt.coffee described.  I guess this would be like the slam roast profile
that you refered to.  However, if I preheat the drum, wouldn't that be like
the alt.coffee message described?  That is high heat at first then a gentle
heat until the end?
Mark Beckman

3) From: Ken Mary
I have recently tried something *similar* to this method to do a quick roast
on some Yirgacheffe. The Aromaroasts have a manual air valve to change
temperature by changing airflow. Leaving the chaff trap off, I carefully
watched the bean bed for proper lifting, and continuously adjusted the valve
to give an *inlet* temperature of 245 to 250 C for the first 1.2 minutes. I
then allowed the temp to drop to about 240 C at the 1.4 minute mark
maintaining 240 C until the end at 4.0 minutes. First crack began at 1.6
minutes and ended at 2.8 with 2 laggards at 3.2 and 3.6 minutes. The cup
profile was very clean and balanced with little aftertaste. Spicy flavors
predominated, but body seemed too light for my preference.
This method may be more important for dark roasts, and I will be making more
roasts to evaluate this further. Sivetz recommends a maximum environment
temperature of 530 F or 277 C. Any higher than this and the structure of the
bean is damaged. One part of the Blackbear process that I have not evaluated
is the equilibration at 230 F. This may be useful for coffees with widely
different sizes like the Yemens. This would be achieved by oven heating,
then dumping into the roaster.
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Ken Mary - Aromaroast - whirlyblade - French Press
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