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Building my first drum roaster
Hi there....this is my first post...i've been lurking for a while, getting some great ideas from all the home roaster projects posted here.

My roaster is still taking shape (actually, its the shape of a welbilt mini convection oven :) ), and i'm still just amassing parts i think might be useful, and i've come to the point where i need to figure out what will be the actual drum. I'd like to get a pound of roasted beans per batch, and i want cooling to happen in the drum (a couple hair dryer fans should do the trick)

Up until this morning, i thought i'd be using a mesh style drum (based on the many variations posted here). however, i found on craigslist some aluminum pipe (8" diameter) and was wondering if a solid aluminum drum was feasible? The aluminum will dissipate heat very quickly for cooling, but will it lend itself to scorching the beans, or can i just ramp the temp softly to avoid that?

i have a great many details to still work out (like chaff collection), but once i get a drum i can plan around that.

Thanks again for all the great info here

Koffee Kosmo
Hi & welcome to HR Mike
Smoke control is another detail to consider
If you want the best of both worlds e.g. heat & cooling properties you could consider light gauge carbon steel

Solid drum is OK in my opinion but you will need a forced exit point for the chaff
For the exit point you can cut slits in the side of the drum instead of holes

Koffee Kosmo attached the following image:

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:
Welcome, Mike!

I've considered the toaster/convection oven type of drum roaster, but all the other to-dos keep getting in the way.

I posted a while back about using the can from a large V-8 juice. It's only 4.5" in diameter and about 7" long, and may at least work great for testing purposes.

I personally think that a mesh would work better. You could accomplish this with aluminum screen, or check out:

KK is right about chaff and air flow.

Are your heat elements above or below or both?

Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
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I'll add another vote for a mesh drum of some sort.

Most toaster ovens or similar are rated at 1500W, give or take a few hundred watts. The rod-type heating elements do not typically react quickly, and from my own experience even at the highest setting tend to take too long (5 minutes or more) just to toast a couple of slices of bread. Using an aluminum drum will require you to heat it up along with the bean mass, which will take quite a long time as aluminum will absorb a lot of heat before it reaches "roasting" temps. Unless you can pre-heat the drum and air inside the oven, you'll have to start "cold" which will push roast times well beyond what you want. A mesh or heavily-perforated or wire mesh drum greatly reduces the drum mass and will allow more convection to occur. Look at the Behmor roaster - it is very much like a toaster oven, with the benefit of being designed specifically as a roaster - it uses a wire basket.

Another way to look at it:

My "roaster's" propane burner puts out 18000 BTU or 5275W. From a "cold start" it takes 25 minutes to reach first crack with just 1 lb of beans at full-power, so I have to pre-heat it to 375F or more to keep roast times in the proper range. Obviously, my roasting set up is not as efficient (no closed cover to help retain heat) but you can see that 1500W is not a lot to work with.
hey, thanks for the tips so far :)
an update on my drum: it won't be solid :) the aluminum pipe i had originally considered fell through, and i got a bunch of aluminum rings that i can make a frame out of, then wrap that in aluminum screen (from the link above).

So, as for heating capacity, i plan to have this run off of 2-3 outlets, and will be adding two extra heating elements from another toaster oven, in addition to the hair dryer heater/fan, and the built in convection fan.

i don't want any shortage of heat and air flow on demand, and with extra fans hope to be able to distribute the heat uniformly (i.e., with out scorching my beans), and dissipate it quickly for cooling.

i won't actually have the oven until monday, so the plan is to have the heating elements along the back side, and possibly on top. i'm hoping to use the bottom as a chaff tray, so i don't want anything to catch on fire down there.

did i mention it will be all computer controlled? i have two electrical engineers (friends, not hired :) ) helping with that part.

so right now, i have, literally, a pile of parts, lots of ideas and help, just waiting for the body of the roaster to show up for the real fun to start
Heya Mike,
Regarding the mesh used in the link: http://forum.home...post_14827I found that the screen was OK for whole beans, however, the ones that are split fall through. I suggest a tighter hole spacing, unless a few split beans aren't a big deal. I didn't want to clean out the roasting chamber after each roast, and scrapped that screen out.
I'll be very interested in seeing your control system, I am pretty lame when it comes to electronics and hope to learn a thing or two.
Tell me and I forget, show me and I remember, involve me and I understand.
jon, i think we're in the same boat as far as electronics are concerned (that's why i have help :) )

i'll share what i learn, and try to get good pics along the way so others can duplicate it if they wish (that is if it works :) )

thanks for the tip on the screen mesh....
ok, a brief update. i just got the oven last night, and its considerably bigger than i expected (roast chamber is roughly 16" wide x 12" x"12" ). my dilemma is whether to up my desired batch size (2 lbs?) or to go with a smaller drum and just fill the extra space up to make heating more efficient. the cool thing is not only that it has a big convection fan, but that it's also got a built-in rotisserie, and for only $15!

The motor i plan to use will be able to handle the added weight, and spin faster if need be.

the oven is rated at 1700W. i'm planning on adding at least two more heating elements for an additional 1200W. is there a way to figure out how many watts will roast X amount of beans?
Edited by itsallaroundyou on 06/24/2009 6:08 AM
Koffee Kosmo
is there a way to figure out how many watts will roast X amount of beans?

It depends on the overall volume
1200Watts X 11 litres volume & insulated will roast up to 600 grams of green beans

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:
thanks for that KK, that's exactly what guideline i my calculations, based on crude measurements, i'd need roughly 4200W for my oven.....that's a lot......i might need a bigger drawing board.....
Koffee Kosmo
For anything bigger than a 1 kg roast (green) its best to use gas

If you reduce the volume you can increase the bean weight but you still need some heat circulation area in the outer chamber


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've got a converted Welbilt that's does a great job of roasting. Maybe you already checked my website. In doing my homework for the build I found out that heating the beans is not the biggest problem in sizing the required power. Heating a pound of green beans from 70F to 400F requires very few watts. The real problem is loss... heating everything else exposed in the roast chamber and then the air outside. Well designed insulation is your best friend.

By just adding 1/8" of oven insulation inside the roast chamber on 5 sides (not the bottom) and new thin stainless sheets over the insulation, the factory heating elements roast 20 oz of green beans to 2C in 15 minutes using only 1400 watts. That's with 5-6 CFM of venting to remove most of the water vapor, CO2 and smoke.
11 years old... forever!
>home-built roasters and fair trade
dbndbit---your roaster is what inspired mine....i didn't even realize that it was also a welbilt, since i looked at your project before i had any of my materials. i notice your drum is fairly large---i was thinking of using one that was between 5-6 inches in diameter if i could find something suitable--do you think i'd be at a disadvantage with batch size and heat distribution?
I have a 5.25 dia by 6.25 high aluminum ice cream maker drum if you want it. It's fairly thin wall, no cutouts. If you are interested, private message me your shipping address & I'll have it on it's way to you.

Best Regards,
Tell me and I forget, show me and I remember, involve me and I understand.
pm sent! thanks jon.....
You bet, on it's way to you tomorrow.
Tell me and I forget, show me and I remember, involve me and I understand.
itsallaroundyou said:
dbndbit---your roaster is what inspired mine...

Glad to be a source of motivation! I knew anybody who looked at the photo of my "prototype" would think: "Dang, I gota be able to do better than that!"

There is a limit on how far you can fill up a drum and still heat all the beans evenly. I haven't looked at it in simulations since there are a lot of forced assumptions and it seems to depend heavily on how the vanes are shaped. But I imagine it will be somewhere around 1/2 to 2/3 full when the beans have reached full expansion. (Roasted beans have almost twice the volume of green beans.) The maximum batch size is helped somewhat by the beans themselves since they provide some of their own heat after 1C.

I do think drum size has a big effect on bean heating. Size matters, and drum volume increases dramatically with the radius. My drum was sized for 2# roasted batch size, and to get the beans closer to both the upper and lower heating elements to get more IR effect. At a little over 7"D and 9"L, my wire mesh drum is about 346 in^3. Bigger than I needed since I wasn't able to roast 2# in my target time of 15 minutes. Maybe if I'd really gone crazy with more insulation?

1# of roasted beans is about 87 in^3 max. So my wild guess is that rcwarship's ice cream maker drum (118 in^3) would be good for roasting maybe 0.9# absolute max (67% full). It would be 73% full if you started with 19-20 oz of green to end up with 16 oz roasted. But the only real way to know how it will roast is to try it!

11 years old... forever!
>home-built roasters and fair trade
ok, here's an update on my progress so far (life has been hectic lately, so i haven't been able to do step by step posts for my progress, so beware---this is a long post!) i will attempt to put pics up soon, but no promises as i'm still swamped.

my convection toaster oven has 3 top and 2 bottom heating elements. we found that they never all ran at the same time with their original wiring, so it turns out running all of them at full power trips the breaker in my house. the good news is that without adding the two other elements i have on hand, i have a lot of heating capacity, the bad news of course is that i can't really tap into all of it in my current house (the washer/dryer is on a dedicated circuit, so will test it there when i get a chance)

Both the top and bottom heating elements are now under separate control, and through just plain luck, my controllers fit into the original control panel (with a little drilling)

I installed fan for exhaust, which is also on its own dimmer (and also fit on the main control panel).

My drum is mostly done. i ended up with a fairly large drum (14" x 5.25") because the cavity in the oven is pretty huge, but also because i'm hopeful some day to be able to do large batches when i have the power to do it). the drum is made out of some aluminum high vacuum gaskets with 2 layers of aluminized steel rain gutter guards from home depot (they were only about $2 for a 6" x 36" piece) rolled around them. stirring vanes are from a veggie steamer.

I bought some 1" mineral wool insulation from McMaster Carr (about $6 per 24" x 48" sheet). It was very easy to work with, though pretty messy, so i wrapped each piece as i cut it in tin foil for easier handling and installation. i insulated the door with some oven door gasket rope. i'm counting on good insulation so i don't have to use my heaters higher than my house can stand. I'm also planning on putting in the reflective flashing inside as dBndbit did on his.

Drum motor is a variable speed lab drill/stirrer. it is way too much power for what i'm using it for, but it was free, and i can connect my drum via a drill chuck. one concern is that this motor's lowest speed is 80 rpm, but i know 60 rpm is near the upper limit.

There are two ceramic platinum heat sensors (also overkill, but they were free). one will be for bean temp and one for environmental temp. these came from an atomic force microscopy company, so i will try to describe them--they are about 1/5th the size of a grain of rice and react to temp changes immediately via a coil of platinum wire encased in a ceramic block. they run on DC so they have each have a 9V battery to power then for the time being. the circuitry only gives me 0.5C resolution, which i think will be fine (i think once i figure out the software i will be able to increase this). i'm still working out how to mount them, but i have a few ideas. these sensors are patched in to a cheap data acquisition card, that runs to a laptop with real time plotting and logging to file (for reopening in excel, etc....)

the main difference with my toaster oven roaster, is that i didn't want to have to deal with anything hot, or have to take the drum out to load the beans so i set it up like a commercial drum roaster that dumps onto an external cooling tray.

so, still to be done is to make the bean loading chute, make the dump door, make the cooling tray/fan, and finish off the drum by installing the vanes and the hardware to mount it to the motor, calibrate my temp sensors and get them mounted...theeeennnnn....i can do a dry run with no beans.....unfortunately i'll be out of town for the next few weeks and won't get to test it before i go :(

definitely want to thank everyone on this site for posting their ideas and projects, since that's largely where all of mine came from.

Thanks again everyone!

"If it wasn't for venetian blinds it'd be curtains for us all"
Woohoooo, nice. Can't wait for the pictures, love to see what you've got going.
Tell me and I forget, show me and I remember, involve me and I understand.
Great idea to wrap the insulation in foil! Easy handling. Might want to be careful not to compress the insulation going over bends and corners or allow gaps between sections.
11 years old... forever!
>home-built roasters and fair trade
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