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Topic: Gene Cafe Roasting Temp and Technical Question (5 msgs / 206 lines)
1) From: Jeremy DeFranco
A few days ago I posted a link to "The Roasting Concepts"
said that the "Sweet Spot" for chemical reactions occurs at a chamber
temp of 401-424. Well today I had tried roasting at 440.  To make a
long story short, I ended up increasing the temp to 455, because I was
afraid of baking the beans. I think next time I will try 450 for the
entire roast. By the way, anyone else with a Gene Cafe experiment with
lower temps? I visibly noticed the shortcomings of the higher 482
roast temps with the Panama 1800, which seems to toast a bit more on
the outside than the inside at this temp. Someone on the list
mentioned it's due to the hardness of the bean. I assume, according
the the book, that lower than max Gene Cafe temps will work better on
all beans- not only by evening out the roast, but optimizing the
chemical reactions as well. Unfortunately, it does not discuss further
exactly how long to keep the roast chamber within the 401-424 sweet
spot range, and when exactly during the roast you want to be in the
sweet spot (before first crack, during, between first and second....).
Anyone have any scientific roasting knowledge to help me out with

2) From: Jim Mitchell
Jeremy -
My hunch is that the Gene is reading the exit air temperature, which may be 
as much as 35-45 degrees F higher than the average bean temperature.
I've diddled around with a number of different settings, and have pretty 
much settled on using a very simple profile of 460 F for the first 14 
minutes, and then either ramping up to 471 to induce 1st crack at 15 minutes 
for beans like Monsooned Malibar,  Sumatra Lintong, and some of the larger 
Africans, or holding 460 for another minute or so for Coulmbia peaberry, 
most Harrars, and a Yemani I really like.
I find it very easy to hear 1st crack if I stand away from the roaster, and 
roughly inline with the chaff collector, which seems to act as a hollow 
resonator, at 5-10 feet, the roaster whine is attenuated, and the cracks 
very audible.
Once the beans have gone through 1st crack, I watch the smoke output pretty 
carefully, which seems to be a better indicator of activity than anything 
else - I try to stretch the interval between 1st crack and cool down to 
3.5-4 minutes by watching the heat element, which glows a dull red in the 
lower right of the roaster towards the back.
I find that I need to retard the roast for most smaller, hard beans, and 
advance the roast for the larger, softer beans - but I can get some pretty 
predictable results now that I've had some practice.
There's a very impressive and distinct jump in the quantity, quality, and 
smell of the smoke as the beans begin 2nd crack - mostly I begin immediate 
'crash' cooling, but for some roasts I just cut the heat and allow them to 
'free roast' for 20-45 seconds before cooling.
Crash cooling consists of place the roaster in its cool cycle, immediately 
popping off the chafe collector (I use a wooden spatula), opening the roast 
chamber cover, using a shop vac drawing from the chaff collector hole to 
accellerate the airflow through the roaster, and directing the output of a 
19" box fan across the roast chamber.
Using this technique, I get fairly consistant 80 degree per minute cool 
downs, which makes for a predictable and managable roast profile as the 
beans drop to 150 F indicated / 190 F actual in about 3.25 - 3.5 minutes.
One note on this technique, if you have a powerful shop vacuum, you may want 
to elevate the left side of the roaster about 3-5 degrees (a nLM triple 
basket under the left edge seems to work well)  which is just enough to keep 
the beans from getting stuck to the output grate by the vac's suction. Aslo, 
a burlap bag of Cedar shavings in the shop vac seems to absorb nearly all of 
the roast smoke, and much of the odor.

3) From: miKe mcKoffee
While I'm not using a Gene Café, but based on 5+ years homeroasting
experience AND info' from watching Tom's Gene Café vid, I'd try max =
temp to
just before start of 1st or first snap of 1st and then drop temp to 440 =
450ish for a good 4 to 5 min or so start of 1st to end of roast.
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4) From: Steven Van Dyke
I'm with Jim - the GeneCafe appears to be reading the exit air temp rathe=
than the actual bean temp.  Makes sense since there's nothing it could us=
to get the bean temp.  Well, unless they built a thermocouple on to the
central divider and contacts on the end plates...
I go with a 482 setting at the start to get the temp up as fast as possib=
 Once the exit air reaches the set point the system starts cycling the he=
so I figure it's best to leave it running full blast until the *beans* re=
the temp I want.
I'm also finding it's about a 14-15 minute total roast.  I'm hitting firs=
crack at about 10 minutes with the exit air temp generally showing about
450.  I'll have to try Jim's trick for hearing the cracks - I've been lea=
over holding my ear close to the gap at the front of the safety shield.
 My problem is telling the cracks from the rustle of the tumbling beans.
Once I get to first crack I've been dropping the temp to 456 since that's=
about the final temp I want.  I also go to watching for the smoke to dete=
the edge of second crack at which time I hit the Cool button.  I'm not cr=
cooling but I've done some tests.  You don't have to pull off the chaff
collector if you put your vacuum's inlet right above the collector's outl=
 It will still suck major amounts of air through the system.  Flipping up=
the safety cover vents some more heat, and running a fan across the assem=
helps too.
I keep wanting to make a 'cooler booster' for the GeneCafe.  I see it as
a triangular piece with a squirrel cage fan inside and batteries / power
cord on the outside.  It's open along one side of the triangle to fit ove=
the chaff collector's opening and on the opposite point to vent the air.
 Flip it on and it starts sucking the air through at a boosted speed.
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5) From: Jeremy DeFranco
Thank You Jim and Mike for the tips. That really helps clear things
up. I think the key must be that 401-424 refers to the AVERAGE temp
the BEANS are "touching". I think when you consider that most of the
beans at any given point in time are touching nothing but other beans,
then the 450-460 makes sense (and even 482 makes sense). I guess the
one thing I forgot to take into consideration is that it is not so
simple to uncover "environment" temperature with a part-drum-part-air
roaster. I think that 401-424 number is more immmediately applicable
to air roasting, which the book pretty much says is superior, because
the heat is way more even, has an infinite surface area (completely
surrounds the bean nearly at all times), and is infinitely close to
the bean. In drum/air roasting (as in the Gene Cafe), the beans are
only really touching either the drum or the air very infrequently at
best, and to be sure, the air flow is not forcefull enough to spread
the beans apart enough to completely bathe the beans. It's an
inprecise final mixture of air and drum I guess- making it very hard
to guage environment temperature. I think maybe it is best to assume
environment temperature (the temp. immediately next to the beans) is
somewhere in between chamber temp and bean temp with the Gene Cafe? I
think realistically, the temperature each bean "feels" within a Gene
Cafe at any given point in time CHANGES from moment to moment, as it
moves to rest against the metal, then to rest against the acrylic,
then to rest against other beans, then a combination of any of these,
etc. This is the reason why air roasting may be superior- the bean
always "rests" up against the same temperature, and same heat medium-
     Best Wishes, and Happy Roasting, Jeremy

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