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Morning Ed, I haven't done any green coffee hoarding yet but am hoping the supplies don't end up like the toilet paper isles!

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Toaster Oven - Convection Roaster Mod

I've been working with a toaster oven I just purchased with digital temperature control. I put hole in the back of it and stuck in a 110 volt A/C motor and 4 inch diameter squirrel cage "crossflow" blower. The motor mounts to to the back wall and I use a hex key to fix the blower to the shaft from the inside. Very easy mod. I spread my beans out on a steel screen 6" x 11" wide in front of the blower.

I just tested a 1/2 pound batch of beans and got to 1st crack in 4.5 minutes with the heat set to 450, then I turned it down to 435 for another 6.5 minutes. It's pretty darn even. I do have chaff ? to blow off but this tells me I should be able to control my batch times pretty tightly. I'm used to little 2 oz batches in an air popper, so this is great. The blower motor I used is not rated to last all that long, It's a class A I think, so this is a good test system. I was afraid to keep the temperature at 450 for much longer because 2nd crack comes quickly. If I drop it to 425 they can be in there a long time. It's amazing the difference 25 degrees makes with coffee beans.

I can share more details if anyone is interested. One more note, the oven itself is convection, but made little to no difference. You really need to move some serious air to heat those beans evenly.
Koffee Kosmo
Are your beans being agitated by the blower ?

I home roast and I like it
Blog -
Bezzera Strega: Mazzer Robur Grinder: 5 Box hand grinders: Pullman Tamper Convex: (KKTO) Turbo Oven Home Roaster: CONA Glass Rod Syphon: Pyrex Brewer:
Can you post some pics, please? Very curious about your setup. Sounds great!
europiccola | yama + coryrod | chemex | AP | clever
wbp1 | wepp1 | bm/hg | co hybrid (still coming soon...)
Nope, not yet anyway. The beans aren't agitated, but it is fairly windy inside the oven. I'm in the process of getting a larger blower that might jostle the beans a bit and further even out the roasting. I'll work up some pictures and post them later.
So, here is my setup. In the first photo you can see the roaster, screen I made for the beans to rest, and the blower way in the back of the oven. The second photo is of the back of the roaster with the motor sticking out. The oven is a convection one, so I might be able to rewire it to use my blower instead of the factory one. I'll have to look at the electronics to see if the motor is coupled to anything.

I also included some bean pictures. The first one, is a 2oz load of beans without the ovens built-in convection turned on. You can seed the gradient pattern of burn beans around the edges and light in the middle. The second photo is with the ovens built-in convection turned on, and it looks fairly even, just a few scattered dark beans. The 3rd photo is a double sized batch of 4oz with the convection turned on. This one in interesting because the beans on right 1/3 are close to the convection fan so they are all consistent and light colored, while the other 2/3 is more like the previous photos. Obviously the convection isn't quite doing its job. The fan is very pathetic. The last photo is of a 4oz load with my blower turned on. It looks fairly uniform, and this same uniformity continues up to a 1/2 pound so far.

Bbriann attached the following images:
4ozblower.jpg 4ozconvection.jpg 2ozconvection.jpg 2oznoconvection.jpg img_0622_800x598.jpg img_0620_800x598.jpg
Hummm, hang a drum on that motor and you have a Behmor.
How are you handing the chaff?
No oil on my beans...
Koffee Kosmo
Without agitation of the beans your are in effect baking the beans
Without agitation you will get uneven roasting / baking

I home roast and I like it
Blog -
Bezzera Strega: Mazzer Robur Grinder: 5 Box hand grinders: Pullman Tamper Convex: (KKTO) Turbo Oven Home Roaster: CONA Glass Rod Syphon: Pyrex Brewer:
I don't think its quite that simple. If you have a huge temperature gradient, then you would have to agitate the beans. But if the temperature difference is minimal, which is what the toaster environment offers, then moving the air around the beans should offer consistent results. The Behmor does the same thing, but moves the beans instead of the air. This more like a fluid bed in a controlled temperature environment if I move the air sufficiently.

As for the chaff, I blow it off afterwards. I can work out a system for that. I like that it doesn't get blown around and stuck everywhere. The inside of the toaster stays nice and clean so far.
Hey Again,

I just made a fine fine espresso using my 2nd blower batch. It was a 4 oz batch set at 450 degrees for 4 minutes until 1st crack, then I dropped to 425 for 5 more minutes. Very west coast medium roast espresso. I can't believe I nailed it the first time. I have another batch that's 425 degrees constant through the roast, so I'll compare it tomorrow.
Koffee Kosmo
Youre thinking is flawed by assuming the heat alone will distribute evenly
However that theory does apply for hot oil deep frying

Reasons are -
The beans themselves can vary in shape and size also vary in hardness, so will roast at different rates unless they agitate
The beans may also have a varied moisture level so will reach first crack at different times unless they agitate

Reference cooking examples
Why does one turn a steak when cooking ? - to cook it evenly
Why does a rotisserie chicken taste better than pan baked
Kentucky fried is finger licking good Grin

I home roast and I like it
Blog -
Bezzera Strega: Mazzer Robur Grinder: 5 Box hand grinders: Pullman Tamper Convex: (KKTO) Turbo Oven Home Roaster: CONA Glass Rod Syphon: Pyrex Brewer:
I just received the thermometer I ordered and tested it on the toaster roaster. The results are very interesting, suggesting the method has much more flaws than even the beans suggest. I had two probes, one in the middle and the other near the front. Without the blower circulating the air, the temperature delta is almost 200 degrees. I had the oven set for 450 degrees and the temp in the middle was about 530 when the heating element was on, while the front one was 330 or so. So, the 450 degrees is very much an average, but the delta is ridiculous.

If I turn on the blower, the delta oscillates between 15-30 degrees, while the maximum temperature is only 415 degrees. And this is when the heating element is on. It drops down to almost 360 at the end of the cycle before the heating element turns on again.

Not good. I'm wondering if the temperature regulator isn't tied to a set cool down period for the heating elements. I was all excited, but I don't see how I can regulate the temperature. The blower can insure a certain delta in the oven, but if the oven itself has a set heating cycle I don't know how to overcome it.

Brian, Heating elements don't need a "cool down." What you are seeing is a 55° deadband from an inexpensive thermostat, probably a bi-metallic strip. While the built-in thermometer might be digital, your thermostat is mechanical. Your only practical option is to replace it with a PID thermostat.

You might want a heat diffuser between the beans and the element. Some of the burned edges might be from uneven infrared heating. But make sure there is a good space between the diffuser and the heating elements so that the airstream can extract its heat.
1 pound electric sample roaster, 3 pound direct-flame roaster, both handmade; modified Mazzer Mini grinder, LaSpaziale Vivaldi II automatic espresso machine. When the electricity goes out I make vacpot coffee from beans ground on my Zassenhaus hand grinder, and heat the water with a teakettle on the gas range.
Yah, I'm going to take the roaster apart today and see how the heating circuitry works. This might just be a great starting point for dipping into Arduino territory and data logging.

I thought about it last night, and realized that the thermostat must assume a particular temperature difference between was is assumed in the oven and the thermostat itself. I messed that up by circulating the air, which is why it thinks the oven is hotter than it really is. That's why it wouldn't get up to 450 degrees again and the element stayed off for too long.

None of this would be fun if it worked the first time. Thanks,
Or, you could put in another heater controller like a variable transformer or percentage timer.
1 pound electric sample roaster, 3 pound direct-flame roaster, both handmade; modified Mazzer Mini grinder, LaSpaziale Vivaldi II automatic espresso machine. When the electricity goes out I make vacpot coffee from beans ground on my Zassenhaus hand grinder, and heat the water with a teakettle on the gas range.
So, I took the oven apart, and surprisingly the temperature control is digital. There are two leads coming off the circuit board to a tiny resistor of some sort. It was covered in a plastic sheath. At room temperature its about 120,000 ohms resistance, and drops to 12000 ohms or so at oven temperatures. It takes a long time to cool off by itself.

I decided to take the sheath off of it so the resistor's (or whatever it is) temperature would more quickly match that of the ovens. That plastic is a good insulator and could explain the delayed response to oven temperatures. So, I tested the oven again. It made a huge difference. Now my two probes are only 20-30 degrees apart, which is way lower than before, where it was almost 200 degrees difference. The maximum was 480 degrees where before it was 530 degrees, when I have the oven set to 450. The low is only 420, so much more in the ballpark.

But sadly, when I run the blower, the temperature still peaks at about 415 degrees which is much lower than 450. The delta between the probes is 7-15 degrees depending on whether the elements are on or not. So, there is an expectation in the system that the temperature in the oven center is about 25 degrees higher what the resistor detects.

I need to do some research on how the different heat controllers work, and go from there.
My neighbor, who introduced me to roasting, was interested in testing out the toaster roaster. He's an avid 2nd cracker, so I knew we couldn't mess up the beans. So, we tried a pound of beans. It took about twice as long, specifically 8min 30 sec to reach first crack, which was not a cracking symphony. And then we let it go for a full 23 minutes at 450 degrees. With the blower on, I don't think my oven gets over 420 degrees.

But nicely, the beans were no less consistent than any of the other batches. The basket swelled up and was 3/4" thick with beans. We stopped before 2nd crack, but they did have a shiny huge. We're guessing it was a fully city + . That's a big load, and I look forward to playing with it some more. I'm surprised the beans in the middle of the basket were roasted at all. Could have been a green bean sandwich with all I had in there.

I wanted to share one last small victory with my toaster roaster. As I might explained, with the blower moving the air in the box, it fools the toaster into thinking its warmer than it really is...and consequently the thermostat turns the elements off, and I get a maximum temperature of 415 degrees when the dial is set to 450.

In the process of understanding the mechanism of the thermal resistor, I tracked the resistance and corresponding temperature inside the oven as it cooled off. I took date points from 400, down to 250 every 25 degrees. It comes out logarithmic, so the change in resistance between 450 and 425 is only 300 ohms, while between 200 and 225 its 5000 ohms.

I had the idea of adding a resistor to fool the thermostat into thinking it was cooler than it really was, which turns the elements back on. And I looked at the data more closely and saw that the curve is fairly linear in the 350-450 degree range. So, I added two resistors, totally 300 ohms to the circuit and tested it out. worked. Now when the oven is set at 450 and the blower is on, I know the maximum is 450 degrees in the oven. And it was still really close for 425 and 400 degrees. As the temperature is lower, my small change in resistance is negligible. The only problem now is that they system could overheat if the blower isn't on. I'll work on that problem another day.

I just wanted to share because the fix was easy, and now I can start playing with roast profiles a bit.
Hey Brian! I'm new to the forum, and new to roasting, but I've got a million ideas running around in my head. Thanks for the post, I think you've been doing a fantastic job of cataloging what you learn.

I've been trying to decide if I want to spring for a toaster oven that has a built in rotisserie feature. I wasn't sure how to move the air around, but the squirrel cage is brilliant! I looked at my dad's toaster, and the rotisserie feature is nothing but a slow turning motor mounted to one of the walls. A simple addition to something like your roaster. That takes care of the agitation, and you've basically got a nice drum roaster at that point!

Of course, then you have to figure out how to make/find a drum. I would lean towards the stainless wire mesh before going with the perforated sheet. I think it can be had cheaper.

Anyway, I'm excited to hear any more progress as it comes!
How are you handing the chaff?good post

toaster oven reviews ==>
Breville BOV800XL Smart Oven 1800-Watt Convection Toaster Oven is the best one known to me so far. It has auto-eject wire rack , removable crumb tray, pizza pan, baking pan, and broil rack included.. It is easy to clean and controls are very intuitive.
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