HomeRoast Digest

Topic: 500 gr. report (18 msgs / 422 lines)
1) From: peter zulkowski
Hi All;
Could not wait any longer.
Found that the problem with roasting a pound of coffee with a Popcorn 
Pumper (1250 Watts) is not the heat availability, but the ability to 
distribute it.
When I bolted the whole Pumper set up to the top of the vibrating type 
tumbler, the beans were all circulating ever so nicely (500 gr.).
Applied the blower and not much changed in bean movement, some dust blew 
Turned on the heat very gently and increased the temperature gently 
taking about 25 minutes for the whole roast.
What I found was that I could boost the temperature, and get to first 
crack, but unless I turned down the heat there was always about a 60 F 
difference between the top of the beans and the bottom; and this 
difference would increase as the temperature increased.
As I plunged the thermometer in slowly, the temperature would rise 
gradually. Pulling it out slowly the temp would decrease slowly; if the 
heat was cut back a bit the temps would even out but toward the low side.
At the end I had about 450 F at the bottom and 370 F at the top. The 
beans were circulating from the vibration, but not fast enough to keep 
the temp even.
This makes a very uneven roast :(
Some of the beans are black and oily, well into second crack, and some 
are rich chocolate brown.. none seem to be uncooked. (probably baked though)
Conclusion: Vibrating the beans while roasting is not the total 
solution. Besides, it is very noisy.
Still need a bigger roasting chamber perhaps. The SS slotted milk-shake 
cup with the inverted lamp chimney on top gets pretty full.
This is probably my worst batch of coffee since I started roasting back 
in October.
Maybe I should stick to smaller batches.
Naaaaa, I will only if I plan to drink it.
Respectfully submitted Monday, January 12, 2004

2) From: AlChemist John
Based on my own attempts, a larger chamber was my conclusion.  I am 
thinking wider and flared, maybe even funnel like, but with restriction at 
the top to help keep the heat in.  Keep at it.  One of will get it eventually.
Sometime around 13:33 1/12/2004, peter zulkowski typed:
John Nanci 
AlChemist at large
Zen Roasting and Blending by Gestalthttp://www.dreamsandbones.net/blog/

3) From: Gene Smith
I was watching a roaster in a Whole Foods Market yesterday and was
fascinated to see the beans shooting up the middle of the milling bean mass,
like a sort of fountain and then falling back.  The part of the roasting
chamber I could see appeared to just be a glass cylinder.  Anybody know how
they get such nice circulation in that cylinder?
Gene Smith
riding the wild learning curve in Houston

4) From: Rich Adams

5) From: peter zulkowski
This is a multi-part message in MIME format.
Hi Gene,
Thank you for your comment :)
Recently I have been thinking about cutting more slits in my SS Malt 
Shake chamber so that some of them blow upward. As it is, I just copied 
the chamber that was in there which forced the air to swirl but are 
angled down about 30 degrees. With trying for larger volume perhaps some 
of them should be directed up. Hopefully that will make the mass move 
instead of just sitting and bobbling. Will let you know.
Still not bored with retirement, here in LHC.
Gene Smith wrote:

6) From: peter zulkowski
This is a multi-part message in MIME format.
Hi Rich,
May I respectfully submit that a simple Dremel tool with a miniature cut 
off wheel works fine for slicing and dicing such objects. You may find 
though, that the malt shake mixing cup is larger.
Hmmm.. I LIKE the idea of double walled though :)
I have a 20 oz. *$ mug that I could adapt... Just wish it were larger.
Thinking about getting more cut off disks, here in LHC
Rich Adams wrote:

7) From: Gene Smith

8) From: Gene Smith
I wonder if a central hole would start the 'fountain' effect, or if some
sort of tube is necessary.  I wish someone had seen inside one of the clear
glass cylinder roasters that are popular with these 'no training necessary'
(i.e., one of your minimum wage employees can do it) units in retail
I have to note, whatever the advantages of various types of roaster, the
'watch it roast' types are very clever for drawing shopper interest in a way
that a closed roaster never would.  I also note that the Whole Foods where
this one is located also vents the roaster with what looks like about a 4"
pipe, and then feeds it into a larger vent pipe - with a gap of several
inches, so the coffee roasting smell gets around in the store without
causing any ventilation problems.  Again, smart.
Gene Smith
riding the wild learning curve in Houston

9) From: Rich Adams
Oh, yeah!  Working with vintage Land Cruisers showed me that.
hmmm, may have to visit my air powered friend.
Rich Adams

10) From: peter zulkowski
Hi John,
Thanks for the encouragement.
Not too long ago were you not doing some sort of a spreadsheet that 
tracked your experiments with roasting. Sorry, I did not pay too much 
attention to that thread at the time, (wife getting her hip replaced and 
all), but I am sure I never saw the spread sheet. Is it available?
Looks like I 'may' have to go to more watts for the heater, but I am 
going to wring all I can out of this little Pumper. 
Oooooo, I found out yesterday with all my antics what kind of a circuit 
my porch outlet is on. All the power stopped at one point, and I had to 
go to the box and reset a 15 amp breaker! And I thought it had had to be 
20 amp.
The chamber definitely has to be larger (just to hold the volume) and 
funnel like seems a natural extension, and a way to hold in the heat. 
Also a way to make the beans move fast enough, and enough heat power, to 
reduce the thermal gradient as much as possible as the roast progresses.
I think drum roasters have an edge on this. All the beans are encased in 
a relatively consistent thermal environment. The only lag is getting the 
heat through the walls of the chamber, and the beans themselves.
Still wondering why I want to roast so much at once, here in LHC.
AlChemist John wrote:

11) From: Chris Holden
On Tuesday, January 13, 2004, at 11:41 PM, "Gene Smith" 
Hopefully. Coincedently I did my first dry run tests last night with a 
laptop hooked up through a serial port interface to a popper to test 
code. Mains power OFF as I don't wish to be the first roaster here to 
report a house fire due to a roaster crash ! It's looking good so far 
in terms of heater control.
I have to admit, as a relative newbie,  it only occurred to me recently 
to use the air flow to actually control the roast temp and I hadn't 
considered its role in minimizing the temperature gradient across the 
roast chamber. I had originally intended to simply drop the fan speed 
by a fixed amount to compensate for the loss of bean mass, after the 
drying stage.
What would you say the relationship between fan speed, heater temp, and 
roast chamber temp gradient is from your observations ? are you simply 
aiming for the minimum airflow to levitate the beans assuming you have 
full control over the temp via the heater ?

12) From: AlChemist John
Sometime around 11:06 1/13/2004, peter zulkowski typed:
Yes.  Ed has kindly put a copy that you can download on his Homeroater 
website.  For whatever reason you can not find it there, I can sent it.  It 
is a minimum fluidization calculation worksheet.
It is definitely a balancing act, just enough of everything, but not too 
much of anything.
And the up front costs.  And, unless you a going to "just" a grill roaster, 
high temperature parts a "fun" to find.  Keep going with the air roaster.
John Nanci 
AlChemist at large
Zen Roasting and Blending by Gestalthttp://www.dreamsandbones.net/blog/

13) From: Angelo
I think you're on the right track. The poppers we use were designed for 
popcorn kernels which have a different size, density, weight and cooking 
time. What might be an optimal design for them might not be for coffee 
beans...Throwing out the popper vane configuration ,and designing a new one 
for use with coffee beans, seems to be the way to go...Keep up the good work...

14) From: Gene Smith
Not to mention the fact that coffee beans don't pop!  Come to think of
it...adding a couple of popcorn kernels to your roast would certainly aid
the circulation of the beans. (:-)
Gene Smith
riding the wild learning curve in Houston

15) From: peter zulkowski
This is a multi-part message in MIME format.
Hi Gene,
My very first roast with a used Popcorn Pumper, roasted for 17 minutes 
(waiting for second crack, did not know what it was) was very well done! 
C said it tasted just fine, better than anything we had been buying at 
the supermarket. However, she wondered how long it would be before the 
popcorn taste would be out of the coffee.....
Might be good for circulation if you  like popcorn tasting coffee ;)
Observing roasting details, here in LHC.
Gene Smith wrote:

16) From: Gene Smith
Well, let's see...there's popcorn shrimp and popcorn chicken...
Gene Smith
riding the wild learning curve in Houston

17) From: peter zulkowski
Hi Chris,
I really had to digest this one, but here goes...
It looks like the temps HAVE to be hotter on the bottom when the 
temperature is increasing, but the goal would be still to minimize the 
difference between top and bottom. Of necessity, the hotter air coming 
in would heat the bottom of the chamber, give heat to those beans and 
give less heat to the ones at the top.
It would be so nice if the beans would circulate fast enough, and absorb 
heat fast enough, that the temp would be equal.
I am not sure if anyone has discovered/discussed the thermal lag of the 
beans themselves, but there has been discussion about differences 
between inner bean and outer bean temperatures, and the fact? that the 
outer bean roasts quicker than the inner bean. Not sure if we can do 
much about that.
It is enough, imho, to be able to provide the same environment for each 
bean as nearly as possible, and the more beans you add the more 
difficult it is to accomplish this.
To get more to the point, fan speed is going to provide heat input and 
bean flow (agitation). In this regard beans in an air flow agitator 
roast quicker than drum roast beans because more of the boundary layer 
is stripped off with the air rushing by. Boundary layer being the tiny 
zone of gas that forms around the bean (or anything) that helps insulate 
it from changing temperatures..
 From my observations, the heater on my popper is nearly always glowing 
red. Hard to measure that temperature with the equipment I have, but it 
drops dramatically when it enters the chamber, so I think this is a good 
place to pick up the temperature, and yes, the temp at this point should 
be compared to the temp higher in the beans, and regulated with the 
heater so that a specified discrepancy is  not exceeded.
Air flow has a factor in this, but since I have learned (the hard way) 
that beans scorch if not circulated very fast, they should be kept 
circulating, but not flying out of the chamber. This is all I know about 
that. Not sure how to do this with a computer.
Could have more to do with chamber design I suppose. It would be easier 
if the beans stayed the same size and density all the time.
But they do not.
They get larger, and lighter, and I suspect that each type of bean, and 
different ages of the same beans, go through these expanding/lightening 
phases at different rates, develop differently during the roasting process.
So this has to be considered if you want to program the air to move the 
beans at a consistent rate throughout the roast.
Even though I do not do all this, the coffee I roast is still pretty good :)
Still confused, but trying really hard. Here in LHC.
Chris Holden wrote:

18) From: Johnny Kent
Around 12:34 PM 1/15/2004 -0700, Peter wrote:
Sure you can do something, you mention what further on below when you talk
about regulating the temperature difference. That's what does it.  Heat
absorption is, in general, proportional to the temperature difference.
My take on the bean scorch is that its more due to contact with the metal
of the roasting chamber.
Perhaps what is needed is to measure the pressure differential between
bottom and some way up the beans.
This could give you a handle on how the beans are lofting. 
But in the end what's fun about all this is that there's still lots of art
to a good roast.

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