BTU to roast 1lbs?

#1: Post by **boublanc** » January 7th, 2014, 2:48 pm

Hello guys
Any idea on how many BTU are required to roast a pound of beans in a drum roaster?
I have built a drum roaster and have in it 2000W of heating power in 3 sets of 700W elements at 110V and it is not quite enough to control the roast properly. according to my calculations I get 6800 BTU.
The drum is 7"x9" made with a stainless steel compost bin. I have perforations in the back of the drum with solid walls. the drum is fairly thin I am guessing it does transfer the heat some what easily but does not have much thermal retention. I load now 300gr and reach 300F in 5 to 6 minutes with the heater on full power, load temp at 400F.
I am now maxed out for 110V, if I want more electric heat I would have to go to 220V. Or do I need to add perforations to the drum walls? Or better yet go to gas? If I do I'd want to make sure I would have enough power.
here are a few pictures of the roaster...

Thank you for your input.

#2: Post by **Boldjava** » January 7th, 2014, 2:58 pm

The USRC 1 lb sample roaster (drum/gas) has 5,000 BTUs.

http://www.usroastercorp.com/images/new ... dffile.pdf

#3: Post by **another_jim** » January 7th, 2014, 4:04 pm

It will depend on the roaster's insulation and efficiency. Boldjava's roaster must be ultra tight; IIRC, the burners on Probat sample roasters are 8000 btuh per drum; and those are designed for 250 gram samples.

For reference, the small gas ring on a home gas range is 8,000 btuh, the medium one 12,000, the big one 15,000, and the rating on a good wok burner is 25,000 btuh.

January 7th, 2014, 4:08 pm

My Diedrich IR-1kg is 8000btu an hour at max. The HotTop uses a 750w heating element for 250g roasts.

#5: Post by **endlesscycles** » January 7th, 2014, 9:24 pm

you could roast a full bag with a light bulb given enough thermal mass, insulation, and warm up time.

January 7th, 2014, 9:35 pm

Thank you guy for the replies.
I am quite surprised to see how much difference there is from one roaster to another...
I have a second compost bin to make another drum as my first one got warped when I welded the fins. So my next move will be to drill holes in the original drum and see how that changes things.

January 7th, 2014, 9:39 pm

endlesscycles wrote:you could roast a full bag with a light bulb given enough thermal mass, insulation, and warm up time.

not with a great amount of control though.
I am able to achieve decent roast with my roaster the way it is now. I would like to get better/faster ramp up to influence the roast better.

#8: Post by **another_jim** » January 7th, 2014, 10:43 pm

endlesscycles wrote:you could roast a full bag with a light bulb given enough thermal mass, insulation, and warm up time.

Easy Bake roaster?

#9: Post by **boar_d_laze** » January 8th, 2014, 12:41 am

Assuming their respective capacities are (roughly) proportional to their respective volumes, note that the 1kg Diedrich's 8000 BTU rating and the 500g USRC's 5000BTU ratings are in line with the each roaster's ratio of drum "skin" (the part of the drum directly exposed to heat) surface area to drum volume.

Arbitrarily assigning a value of "1" for the USRC's volume, and doubling that to "2" for the Diedrich, gives us respective ratios of surface area to volume of 1:1.4, while the ratio of BTU ratings is 1:1.6.

BDL