HomeRoast Digest

Topic: 800gr to 666 in 18 minutes (5 msgs / 163 lines)
1) From: petzul
35 MPH gusts out on the patio today, white caps over on the lake, but I 
want to roast anyway.
The outside temp is about 65F, a bit chilly with the wind.
Thanks to all of you who reported that long roasts are not necessarily 
bad roasts.
Today, with my still not finished Turbo Beast I roasted 800 Gr of decaf 
in one batch.
It is not finished because it is not fully insulated (only about half), 
and the control panel is hanging off of it again because that gets too 
hot when mounted on the side.
I am in process of making a more permanent case to hold it all together. 
No more screw clamps!
To do full capacity roasts  I will have to modify the stirrer a bit. 
There is still plenty of power and speed, but after 800 Gr they do not 
fly around as much.
I dumped beans in slowly until it looked like they were not mixing very 
well and took some out until they were.
The resulting batch was 800 Gr.
This roast taught me a bit more about roasting that I would like to share.
No preheating this time, and it took 7 minutes to get to 300 F.
The TC was varying about 6 degrees during the rise, which I attribute to 
the mixing inadequacy.
First crack started about 385 F, so I checked to see if the stirrer was 
still attached.
Yes, everything fine.
Maybe because it was the decaf? or the temp difference between the 
bottom (where the TC is) and top of the roast?
I turned down the thermostat, and first crack continued, right up to 
about 410 F. Then tapered off.
The TC was reading steadier at this point so I suspect the bean temp had 
come to equilibrium.
I started to increase the power and saw the temp fluctuate again, and 
second crack started. I cut the heater power but second crack continued 
and the temp kept climbing.
This occurred over several minutes.
When I finally decided to stop the roast at 18 minutes, and removed the 
convection oven, the beans were a rich dark brown with just a hint of oil.
The surprise I had during this roast was that it finished quicker than I 
had planned.
What I wanted was to hold between 1st and second crack a while longer, 
and keep the roast going for a full 20 minutes.
But it got too hot. That really surprised me.
The beans did expand as expected. So now I need to get larger bowls to 
dump into; for now I will just use two of them.
That's the news from Lake Havasu City,

2) From: AlChemist John
Sometime around 13:27 3/26/2005, petzul typed:
I like that bit of information - I am running my ZenII roasts 16-18 minutes 
right now.  Exceeding smooth cups.  I am to try a Kenya next and see what 
it does to that brightness.
Why did you decide to do that?  Seems like a preheat would give you a more 
even roast as you have heat everywhere. so less temperature swings.
I think the lack of preheating.
I won't mention that some people hold the belief that there is an 
exothermic stage in between 1st and 2nd crack.  I also won't mention 
whether I am one of them :-)
Thanks for the update.  I need to get a "what I have learned with my ZenII 
roaster" post together.
John Nanci 
AlChemist at large
Zen Roasting , Blending & Espresso pulling by Gestalthttp://www.dreamsandbones.net/blog/http://www.chocolatealchemy.com/

3) From: petzul
This is a multi-part message in MIME format.
Sometimes my thermocouple reading jumps around 4-8 degrees, no matter 
what size roast.
This happened since I mounted the GG in a steel lid. Never happened when 
it was a glass lid.
Checked the volts to ground on the SS bowl and got about 4V AC.
Could this be the reading problem?
It doesn't happen all the time, but did again with the half pound roast 
I did a bit later.
Lots of the coffee stain on the rim of the ss bowl so I guess contact 
with the GG is intermittent.
When I insulate it finally I will make a silicon gasket to keep them apart.
I did not preheat because the beans bring the temp way down anyway, and 
I wanted to see how it would work with no preheat.
You could be correct about the exothermic.... had it happen before and 
forgot to consider it.
Nice to know you need less power input at the end of the roast :)
AlChemist John wrote:

4) From: Aaron
Thermocouples are very sensitive devices so they can easily jump a few 
degrees in a dynamic environment like a roaster.  I don't think the 4 
volts is what is affecting it.  If it's a thermocouple then it's 
voltages it runs on are in the millivolt range.  4v would way overload 
it.  If the thermocouple is being bumped by beans and stuff while 
measuring, that can make it jump around a bit too, depending on how 
'tight' the twin pair is twisted together.  If it is an RTD now, it runs 
off resistance, and the voltage while it would not affect it, any voltge 
being induced into it would throw it way off.   Then again you could be 
developing a slight static electric charge on the lid as well which 
could possibly cause this.  What you might want to do is run a small 
wire from the steel lid to ground.  maybe something with a clip on each 
end so you can easily attach / remove it for cleaning.  If you are going 
to use the electrical sockets ground to connect to, be absolutely 
POSITIVE you are hooking to ground, and not neutral.  While in theory, 
in a perfect working system, these two should be the same thing, in real 
life, you can be in for a very nasty suprise assuming your neutral is at 
ground state.
Another thing to consider,  a good thermocouple can cost upwards of $100 
or more.   They can also be found for $5 or $10 dollars.....  obviously 
performance between the two is going to be umm  different.
Don't know if this info will help you any but it might give you a place 
to start looking to solve the problem.
petzul wrote:

5) From: Ken Mary
You should not forget that an unshielded t/c wire may be affected by the
heater EMF. The reading will vary in a random or cyclic manner. But the
initial extreme variance is due to regions of high and low temp beans moving
past the t/c. I see this in my infrared readings during a popper roast.
During initial heatup, my readout will vary +/- 10F. But by the time the
beans reach 400, it is +/- 1F. The same happens during cooling, at first the
reading is +/- 5F then quickly becomes +/- 1F. The IR field of view is about
2 inches diameter at the top of the beans.

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