The maker of my new coffee roaster reccommends (insists upon) letting the roaster rest and cool down between consecutive roasts to lessen the stress on it. I roasted 2-3 batches in a row on an older machine, and it did indeed show much stress. In fact it began to disintegrate at some points where the temp. was highest. It’s still useable, though.
Backl to my question;
Roast time is 10-15 minutes/batch, and temperature inside eventually gets up to maybe 450F. It seem’s to me that 2 or 3 cycles from ambient to 450 and back would be more stressful than a sustained 30 - 45 min period of temps of 250 - 450F. Experimentation, while fun, would be kinda expensive.
The roaster is made of stainless steel, glass, and high temp plastic. And it works pretty good.
Peace,
mangeorge
The interior of your roaster oven is no doubt designed to handle 450°F, however the outside bits, including the case, electronic timer etc. are not. The longer the oven is on, the more heat will be transfered to these sensitive bits, the hotter they’ll get, and the more likely the oven is to suffer meltdown.
It’s one of these. The I-Roast.
The heated air blows up through the green coffee beans in the glass chamber. The bottom doesn’t really get hot at all, just the top.
Here’s an image from one of that patents (6,324,770) at the bottom of the spec sheet. All the other patents show a similar design for the bottom part of the dryer.
You’ve essentially got a blowdryer in a confined space down there, and if you run it too long it’ll start warming the non-pyrex pieces. Overheating is a big problem in blowdryers, and they don’t have electronics built into the housing.
There’s also a lot of attention devoted in the patents to the seal between the glass and the base. That suggests that the seal design was troublesome. Perhaps the silicone won’t stand up to prolonged heating? That gasket gets a lot of mechanical abuse in addition to thermal cycling. The combination of stresses could cause problems over the long term.