After my airpopper died I left roasting alone for a few years but then I sourced fifty pounds of coffee from here: http://www.sanlucasmission.org/ and got into using a heat gun/bowl setup but was wondering how I could roast greater quantities well. I even tried roasting over a fire. I purchased this bread maker for a few dollars and started considering how to modify it into a roaster. I really like to see the color changes as roasting occurs so did not consider the gas grill option despite its greater heat control possibilities. I noticed the excellent homemade roaster of farmroast on home-barista and decided to add the convection oven.

The bread baker control panel is removed. A switch controls the fan for air input ( I just use it to cool the roaster post roast but wanted originally to remove chaff that way). Another toggle switch controls the rotation of the agitation blade. A friend wired a circuit which is adjustable by a potentiometer the timing that the bread maker's element is on versus off to control conduction heat. I can also control the degree of heat that the convection oven delivers. A local air conditioning/heating place was able to weld the stainless steel cone to allow me to combine the two parts of the roaster with minimal environmental air entry.

I use a digital thermometer from Omega to measure temperature near the BB element and a second probe to measure temperature at the bottom of the cylinder.

To stop the roast, I remove the CO, and dump the beans into a large SS bowl then into the long screen you see in the image. Thanks to some insulation I placed within the shell (provided by another HBer (thanks!) I can touch the white shell of the bread baker but I do have to use mitts to hold it long enough for the dump. Currently, I roast under the oven vent and take the beans outside to cool (very fast in the current cold weather). With 340gram roasts chaff generationl is a problem but I've yet to roast well into second crack. If the temp were 50 F at least outside I would try it. I have to blow out the chaff between roasts.

Once again, thanks to the Home Barista posters and forums for lots of fun ideas to try and implement. After 9 roasts, it is too early for me to tell if I will achieve roasts adequate to justify using this rather than UPS/FedEx and the many excellent professional roasters mentioned here.

Nice work chert

I also have a Hybrid Turbo Roaster of my own design
I love the TO concept so much I have designed a kit

KK

Thanks for the input KK and farmroast.

I will look for some thread about convection oven roasting, but what drop in temperatures do you find useful with the CO? Do you have any addition of conduction heat?

The motor obscures any pops from first crack. How do you sense first crack in yours? Second crack is much louder. However with the roasts I've done at 350-450F ET ramped up in steps with stopping 1.5 minutes into second crack there is no oily sheen on the beans despite my bean probe measuring 435 F. Am I mistaking second crack for first?

Where do you find is a good place to measure bean temperature? I am currently testing various locations to measure bean temp. My initial location was at the base of the roast cylinder, but I think I need to move the probe further into the bean mass. I am concerned that the life of the thermocouple will be short, however from agitation of the beans.

Any input from home roasters would be appreciated.

Any

I have found that volume is the most important factor 6 to 10 litres is best

I have roasted over a hundred batches on the original prototype roaster


Agitating beans


Chaff collection



Beta testing on the kit roaster will commence in the New Year

KK

Thanks for sharing your experience!

FWIW, more documentation of my tests with this Frankenroaster:

I have pounds and pounds of some green coffee that I have not roasted to my liking. I have been trying light or cupping roasts which are all disappointing. So I am running tests with the stuff. Later, I will roast it well into second crack to see if its drinkable at later stages, but at less than Full City +, I have not found it worth drinking. On the other hand, SM El Salvador Orange Bourbon and Paradise Roaster's MVP 2009 are tasting nice roasted with my setup, so I continue experimenting. Before buying more good coffee to roast, I want to have a concept of how to utilize the roaster for temperature control.

Today I roasted 600 grams to see what a larger mass of beans would require for time. I set the convection oven set at 450 F and the conduction element delivering 408 F. Drop in temperature was 150 F and the roast reached 468 F at 22 min. Second crack was roaring along. With that mass of beans and briefly stopping agitation, I was able to hear 1C. I think this shows that the combination provides enough heat for roasting around a pound at a time. (I threw this batch out because I had added some more insulation and cement outside the roast chamber which I thought probably needed to cure/outgas away).

Next I roasted 275 g at the same setting with drop in temperature of 257 F. At that lower mass, my TC was not deep within the swirlling beans, but at the air/bean interface. For the first 3 minutes, my reading fluctuated +/- 7.5 deg F than settled down to +/- 4 for two minutes. After 5 minutes, it gradually increased without fluctuation until I stopped the roast at 436 F 1.5 minutes into 2C. The beans are somewhat mottled with no oily sheen.

Next I roasted another 275 g batch. As I was preheating the roaster, a neighbor knocked at the door and the roaster continue to heat up, so the machine was at 390F at drop in. I assumed that the load of coffee would decrease the temperature, but my probe only declined to 377F before gradually increasing. It read 468 F when I stopped the roast at 8 minutes. Either the air and metal within the roaster can store quite alot of heat, or those beans are fairly dry, I would thinks.

Update: The Frankenroaster is a bust. I roasted 96 batches since I completed the roaster in December, most around 425 grams but today the BB motor broke down.

It will probably be many weeks or months before I rehabilitate or redesign the thing just due to lack of time. I have enjoyed the process and the home-roasted coffee and espresso very much. It has been great to inexpensively share fresh-roasted coffee with others in my community.