I have been home roasting for about 4 years (home made Corretto) and recently purchased a 1kg electric drum roaster that has two 1500w elements. It has two stock digital temperature controllers that read drum and exhaust pipe temperature. I added an additional two thermocouple probes in an effort to also read bean mass temperature, and also temperature near the top of the drum by the exhaust pipe. In retrospect the latter probe probably wasn't needed but I am finding the BT one useful even if it 'appears' to be 10 to 20 degrees off (first crack usually around 183 degrees on multimeter).

It also appears that I do no have variable temperature control. I can set max. temp (set point) on the 2 stock controllers but I do not think I can adjust the output of the 2 electrical elements on the fly and therefore directly regulate drum temperature for different types of beans and roast profiles. What I am left with is using the valve on the roaster's horizontal exhaust pipe (closed to fully open) to regulate exhaust air flow. Initially I thought having it closed would increase the temperature inside the drum but it actually appears to have the opposite effect. When I open it, the temperature inside the drum tends to increase more rapidly. I obviously need to read up on all of this and how to get the most out of this type of roaster. The 'manual' simply states leave the exhaust valve mainly at 50% and open it fully towards the end of the roast. Can someone point me in the right direction? I've done a few searches but not hitting a bull's eye. Thanks.

Cannot comment on the heating element, but opening the vent/damper initially increases convection and temperature and rate of rise. By opening the damper more, like fully open, more cold air is drawn into the roasting chamber, and the temperature will decrease. So roasting will be to find the ideal setting/balance of opening the damper and adjusting heat.

I have been contemplating the air flow for a while now. The air flow can be measured with an air speed meter, pressure gradient gauge, or mass flow meter; still have to decide on an ideal method.

Thanks. I've had an opportunity to read up a bit more on convection, conduction, etc. during drum roasting. One of the things that has me puzzled (one of actually a few things... ) is that if I open the exhaust damper more fully, thereby increasing air flow and convection, but drum temperature actually begins to drop after an initial spike/temperature gradient increase because more cool air is being introduced into the drum chamber why would roasting time be shortened? I assume roaster's that have adjustable heat source whether gas or electric can compensate by turning up the element or gas dial at this stage, but my roaster doesn't have this ability. From what I have seen it is much like a 1kg Toper Cafemino which is also built in Izmir. Not sure if the Toper has the adjustable exhaust damper like mine, as the review I read didn't show one.

I think... I'll roast 2 back-to-back 1 kg batches of the same bean this afternoon. I'll keep the drop temperature the same for both (still haven't quite figured out what's best yet for 1kg), and then do one roast wheredamper tends to be more open and one with it more closed, and compare. To date I have been keeping the damper 75% closed for the first few minutes of the roast, then opening to 50% until first crack, at which time I open fully until the snaps of second crack before dumping. On average first crack tends to arrive around the 9 minute mark for most 1kg roasts and second crack about 4 minutes later. Unlike my previous little breadmaker/roaster set-up I'm finding it difficult at times to determine end of first crack as the second stage seems to be flowing into the first much of the time. There doesn't seem to be a period where things settle down after rolling FC.

Buschy wrote:I assume roaster's that have adjustable heat source whether gas or electric can compensate by turning up the element or gas dial at this stage, but my roaster doesn't have this ability.

It has 2 1500w elements that have no ability to adjust? Just does a fast sample roast with the exhaust damper for tweaks and chaff?

It has 2 1500w elements that have no ability to adjust? Just does a fast sample roast with the exhaust damper for tweaks and chaff?

Yup, the Emko controllers it uses are a simple on/off temp controller. Turns elements off once they reach a pre-set temperature, turns them back on when they drop below it, so learning how to use the exhaust damper effectively important. The exhaust system has a dedicated motor postioned at the end of the exhaust pipe that sucks air towards the chaff collector.

The heating element switch on the control panel has 2 settings. When set at (1) it turns on the first element, when set to (2) turns on the second one. That's about the only thing you can adjust with respect to the elements while roasting. However, with only one element turned I believe you are heating one half of the drum more than the other given that the elements sit side-by-side below the drum.

I'd think of modifying the elements control. There are members here who could suggest the best way to do it.

Hello Ron.

I have a Cafemino electric and what you described is pretty much what it is with a stock electrical toper machine. When you open the vent the air flow forces all the hot air (energy) that was still around the element below the drum to go through the drum/bean mass and increase the temperature. But, as Henry said, this is a transient condition and the air temperature will decrease, or at least not increase as fast, because of the increase heat extraction.
With a roaster that has no control over the energy output the only control you have over the profile is indeed through the air flow damper. I find it very difficult to control the profile with only the damper. I personally keep the damper fully open for as much of the roast as I can. I do this for two reasons; maximum extraction of chaff and maximum heat transfer through convection with the bean mass.

To improve the control and not rely only on the damper, I have installed a potentiometer controlled Pulse Width Modulator that acts pretty much the same as a dimmer for the resistive load that the elements are. The controls are not as fast as a gas burner but with a little practice and some anticipation one can achieve just about any profile.