HomeRoast Digest

Topic: update on TB meltdown (5 msgs / 145 lines)
1) From: petzul
Well, I sure hope someone is learning something from my experiments 
besides me.
Yesterday I rebuilt the stirrer, reassembled it with hi temp silicon 
rubber and started to cut a hole in the Pyrex lid with my Dremel.
Well I was taking it easy, very much aware that Pyrex does not 
necessarily like having holes cut in it, and after a half hour or so I 
just had to get a cup of coffee!
I put the GG down on the bench gently and left.
When I returned all the Pyrex had spider webbed. Looked like a broken 
Someday I will learn about leaving from what I am doing in the middle. :-(
So I looked in my 'spare parts' and came up with a Plexiglass convection 
oven top. Unfortunately, the GG is the only one I have over 1400 watts, 
so I adapted this plastic unit to fit the GG heater assembly with my 
Also cut another hole in the top and mounted a 750 Watt heating coil in 
it, bent so that it almost touches the bottom of the GG.
Plenty of clearance for beans underneath :-)
Today all the red silicon had cured so I had to test it.
First I plugged the heaters into my 20 yr old 15 amp circuit and let it 
heat up.
Now 1440 for the GG and 750 for the auxiliary should have popped that 
circuit breaker, but it did not.
Perhaps I should have an electrician look at it, or maybe these wattages 
are over rated, but the circuit handled it fine.
I had not yet thrown out the beans from yesterday, so I just tried my 
first roast with the new set up with those.
Not sure whether to pre heat or not, I decided to warm it up to 270 
before I added the beans.
The stirrer held together fine, and the temp first dropped to 160, then 
started to climb.
300F in under 2 minutes, and first crack in under 5 minutes!
I should mention that when it got to 400F I turned off the auxiliary 
heater. This did not seem to matter, at 430 I started pulsing the main 
heater, but the temp still continued to rise. At 440 F I turned off the 
heaters and the temp still shot up. In less than 7 minutes total the TC 
read 454, and second crack was well under way, big time!
I had to take the top off and cool it with the hair dryer to avoid 
another meltdown.
It seems to me that the heating coils must be well over 400, and still 
give residual heat even though they are turned off. So, I need to turn 
them off sooner, or pulse both of them.
Looks like it is controllable and can roast some great coffee.
Will try that this afternoon.
Reporting the news on coffee roasting, here in LHC.

2) From: Brett Mason
Monster Garage has little to offer the list that we don't already get
from our more adventurous members!
Carry on!
On Wed, 09 Mar 2005 12:02:51 -0700, petzul  wrote:
Brett Mason
   _(( )_  Please don't spill the coffee!

3) From: AlChemist John
Sometime around 11:02 3/9/2005, petzul typed:
Have you tried drilling with an abrasive bit with the Pyrex in 
water?  Keeps it cool and should let you drill it right out in  a minute or 
two.  You can't use a spiral cut bit though, just flings the water out.
John Nanci 
AlChemist at large
Zen Roasting , Blending & Espresso pulling by Gestalthttp://www.dreamsandbones.net/blog/http://www.chocolatealchemy.com/

4) From: Ken Mary
If the beans can see the heating element, they may be getting overheated. I
am not familiar with the physical size of the heater, but it may still
radiate a lot of heat after it is turned off. You should be switching the
heat earlier, or raising the heat in steps from the start so you have better
control. For example, preheat and load the beans, then try to stabilize at
an intermediate temperature. Now since the roaster is under control, you can
gradually raise the temperature until you reach the roast degree that you
want. In my drum roasts, I am now setting the first control point at 380 F
which is just short of first crack. After waiting at 380 to allow drying and
bean to bean equalizing, I can very easily control the ramp through first
and up to second.

5) From: petzul
Thanks Ken for your input on this, and your other contributions to the list.
The beans do 'see' the element, and I am afraid they are getting 
overheated, they have a burnt taste (yuck).
In the GG the heater is 'hidden' behind a grill, and just the hot air 
gets to the beans.
Back to square one again. The other problem with the aux heater, it kind 
of melted my hi temp plastic convection oven top!
That may contribute to bad bean taste also... again yuk.
AT any rate, I have decided that I do not need an  auxiliary heater 
unless I can shield it. When I checked it with the pyrometer it easily 
gets to 800F, but not to red heat. Still a bit much for plastic.
Also the plastic convection oven is not very good for temps I am likely 
to hit in biasing for a fast
rise time to 300F. The thermostat in the convection oven shows internal 
temp of the GG up over 500F at the end of the roast ( I took the stop 
off the thermostat so I could crank it up).
Next step is an aluminum plate on the top of the chamber (nothing too 
serious, a serving tray) to mount the GG in;
more insulation, and I would like some kind of a window so I can see 
what is happening.
Although a window is not really necessary.
Sound and smell works pretty good for me at this stage.
How long does it take you to do your drum roasts? How big a batch can 
you do?
Need to fix this soon, almost out of roasted beans.. here in LHC.
Ken Mary wrote:

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