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Topic: How does the HotTop work? (7 msgs / 312 lines)
1) From: Maryann & Dave Schellenberg
I've been using a HotTop I bought used for about 10 roasts now.
I'm always happy with the first roast of the day.
The second one can be a problem due to not reaching a high enough 
I've followed the advice of those on the list about how to prepare for 
the second roast i.e. cool with tray, cover, and filter out, and then do 
a second cooling cycle.
I still can't get my beans over 412 or 413F on a second roast of the 
day. The roaster seems to max out at this temp, and while it will 
continue for three minutes or so at this temp, that seems to me to 
qualify as a stall.
I am in contact with HotTopUSA, and they are helpful.
I would like to develop a good understanding of how the HotTop works so 
I can debug this thing myself, rather than installing various new parts 
to see if that will help.
There is a fan in the unit which blows out through a filter on the end 
of the unit.
It turns on and off during the roast, and I have no idea what the 
criteria are for turning it on and off.
Anyone else know?
The filter is supposed to be good for about 10 roasts. What are the 
signs that it is time to change this filter, other than counting the roasts?
Since the heating unit is turned on and off during the roast to maintain 
some sort of preset profile, what function does the fan play in 
following the profile?
There is a temperature sensor on the end wall of the drum cavity, and I 
can see what it is indicating by pressing a button.
I have drilled a hole in the bean chute cover so I can insert a 
temperature probe into the bean mass.
For the first 3/4 of the roast, the sensor temp is higher than the probe 
Then there is a crossover point, and for the last quarter, bean temp is 
higher than sensor temp.
How can this be? How can the beans continue to rise in temperature, when 
they are already hotter than the drum cavity?
I'm thinking that some people must know the answer to these questions; 
if Jeffrey Pawlan can build a computer control for this roaster, then 
there must be some understanding of how it works.
Care to share?
Dave S.

2) From: Douglas H. Boutell
Maryann & Dave Schellenberg wrote:
That's the exothermic reaction taking place from the chemicals in the beans.

3) From: Michael Boshes
What roast level are you aiming for? What state are the beans in just before
the machine shuts off? Have they entered 2nd crack? A minute into 2nd? Or
more than that? I find it hard to believe that a correctly working hottop
would shut off within the roast range that most of us prefer our beans.
What is the voltage at the power outlet? If it's too low the machine may
have to work too hard which may cause the shutdown at the height of the
What weight of beans are you using? Using more than the suggested 250 grams
is one way of prolonging the roast if it is getting too hot or you want to
roast to higher temperature.
Filter life is 30-40 roasts according to hottop manual. I find only the
bottom half of the filter turns black with use so I flip the filter top to
bottom at 20 roasts and then replace at 40.
The button sensor reads the air at the back wall of the machine, pretty far
removed from the heating coils. It is not a reflection of bean temperature
but it is incredibly consistent roast to roast. In my setup 1st always
starts about 395, gets quiet around 405, gets into 2nd around 410, and for
the few times I get into rolling 2nd I eject at about 414, but I usually
push the button around 411.
Moving a sensor to a different part of the machine will give you different
readings. Not more or less accurate. Just different. If the readings are
consistent roast to roast they can help you roast better. One thing I've
experienced when using probes in various places in the hottop is that if the
probe is too close to the heating coils you could actually be picking up the
heat of igniting chaff later in the cycle.
On 6/22/06, Maryann & Dave Schellenberg  wrote:

4) From: Maryann & Dave Schellenberg
Michael Boshes wrote:
For most of my roasts, FC+. Occasionally C+ or FC. One roast, with SM's 
French Roast Blend, French.
On second roasts, the beans never get into second crack.
I power my HotTop through a variac, which I monitor with a digital 
multi-metre. I set the variac to produce 120 volts minimum, which 
happens when the heating element is turned on. When that switches off, 
voltage reads 125 volts.
I weigh out 250 grams for almost all roasts. The exception was the 
French Roast Blend, when I expected to have trouble getting the beans 
that far; for that experiment I used 200 grams, and since it was the 
first roast of the day, it managed.
That's a point I would argue. I began roasting in a Poppery, with a 
thermometer probe in the bean mass. I know what bean temperature I want 
to achieve. I don't really care about the temperature of the air at the 
back wall of the machine, only the temperature of the bean mass.
I used the location shown at http://www.quiknet.com/frcn/Coffee/HowToHottopTemp.htmlThis side of the drum is where the beans pile up, opposite side to the 
heating element.
Thanks for your comments, Michael.
Could you tell me about your experiences with back-to-back roasts?
SM's description of the HotTop http://www.sweetmarias.com/prod.hottop.shtmlmentions getting different results from a warm start than from a cold 
start but stops short of saying that it won't get to second crack on a 
warm start.
Dave S.

5) From: Cameron Forde
Hi Dave,
If I let my Hottop cool for about 45 min (with chaff tray, filter, and
bean chute cover removed) between roasts I have no problem getting to
second on subsequent roasts.  My voltage from the outlet without load
is 118V.  I've also changed the filters and am using the green scrubby
pad mod that someone on the list suggested (I think that there is more
air flow and thus more cooling with these "filters").  I do roast
indoors with stove fan running (21C).  It sounds to me like there is
some repair needed to your machine.  However, I don't know if the
problem is with the heating, sensing, or controlling systems. The fact
that your first roast works suggests that the heating system is fine
-- my first hunch would be that it is the thermal sensor (have you
cleaned it recently?  I think that it "reads" high if it has a coating
of roastium).

6) From: Mark J Bergh
I will give you the knowledge of events encountered with my new Hottop
Digital over the past few months since purchasing it.  Perhaps it will give
you some baseline for comparison.  I generally run 3 back to back roasts at
a time allowing the requisite cooling period between.  In my dealings with
Michael at Hottop USA, I find him technically knowledgeable and very
responsive and helpful.
My unit functioned perfectly out of the box with 118v household voltage
unloaded; I also use a Variac (with Fluke DMM to monitor) and, like you, set
it for 120V under load which cycles during the roast to as high as 125V when
the heaters are off.  I notice the fan comes on and changes frequency during
various stages of the ramp-up cycle, apparently to tailor the cycle and soak
of the roast profile. 
The drive motor abruptly stripped the plastic gears in the reduction gearbox
to which Michael sent me a new motor assembly literally within 3 days of my
notice.  An easy repair which allowed exposure and observation of the inner
workings of the unit.  Not too complicated!
Around roast log entry 18, the unit abruptly shut down prior to achieving
first crack and went into cooling mode.  Michael indicated it was a thermal
overload and the protection system had initiated the cooling cycle.  He had
me run tests observing temps (indicated by the digital readout on the panel)
every 30 seconds using a known bean type.  I believe it was a Sumatra
Mandheling I used.  Results were the same with the unit shutting down prior
to achieving first crack.  I then tried house voltage (without the Variac)
and re-ran the test.  The results allowed the full cycle but never achieved
the temps necessary to finish the roast.  That is when I decided to change
the filter element.  This brought the unit back to normal and I have not had
a problem since.
What I have learned about this machine is that the filter is an integral
part of the roast temp profile and if too free flowing, it will not achieve
temps desired; with an obstructed/clogged filter, the temps will prematurely
rise triggering a protective shutdown.  Additionally, as you and others have
noted, a full 120V at the heater "ON" condition is necessary to achieve the
temps necessary to fulfill the roast in the time period programmed.
I didn't catch whether you have a digital or analog model but I have also
found that I must program the MAXIMUM time allowable into the unit at
startup to enable me to control the termination point of the roast where I
dictate.  You can set the digital model to a full 21min59sec and have 5
additional 30sec add-ons at the end of the roast if desired.  You should
never need more time than that!
I questioned Michael whether the sizing of the heater elements varied in
manufacturing batches and he informed me that they were selected by
resistance for uniformity.  Enough said there.  I still think the heaters
should be capable of achieving a full roast profile on unaided household
voltage of 110V min to 120V max.  It seems though that the Variac is a must
have for the Hottop.
I just ran 3 roasts yesterday with the third SM Puro Scuro at Vienna
(rolling through second crack); all turned out perfectly!
I will appreciate following your developments,

7) From: javafool
Excellent information and very well written!  Thank you for sharing. I
discovered part of this information on my own but you have added
considerably to that knowledge.
I almost always roast 8 ounces of coffee per batch because I don't have =
good use for the odd amounts of beans I have left from 1 or 2 pound
purchases. I usually finish my roasts at 17-18 minutes but don't know =
the line voltage is. I just never had a problem so I never checked. I =
set my HotTop on 7 and press the eject pad when the roast is where I =
want it
to finish.

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