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 temperature. 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 temp. 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.
Maryann & Dave Schellenberg wrote: <Snip> That's the exothermic reaction taking place from the chemicals in the beans. Doug <Snip>
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 profile. 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. MichaelB On 6/22/06, Maryann & Dave Schellenberg wrote: <Snip>
Michael Boshes wrote: <Snip> For most of my roasts, FC+. Occasionally C+ or FC. One roast, with SM's French Roast Blend, French. <Snip> On second roasts, the beans never get into second crack. <Snip> 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. <Snip> 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. <Snip> 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. <Snip> 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.
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). Cameron
Dave, 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, Mark
Mark, 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 = a 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 = what the line voltage is. I just never had a problem so I never checked. I = just set my HotTop on 7 and press the eject pad when the roast is where I = want it to finish. Terry