I am experimenting with my first roasts, first one was in a mesh over an open flame and my second roast in a converted Illy can rotated by an electric drill over a stove.

The second roast is much more even and I learned a lot so far, the first was underdeveloped and too light so the espresso was a sort of battery acid, my second roast took waaaay too long (20 mins) but looks much more even and is of the right color (FC+)

I'm thinking about making a simple drum roaster but with a load of approx 90-100 gram of greens the Illy (designed to contain 250g) can seemed quite underfilled, which got me thinking...is there an optimum between drum size and load?

I have a piece of 150 mm stainless duct that has it's new destination written on it but I wonder if it's too large for my needs. i use approx 1 kilo of beans a month, so I would ideally roast in smaller batches of anywhere between 250 and 500 g or there about.

There is a formula for finding your drum size vs load. Let me see if I can find a link.

Found it- Roast size (ounces) = Drum Volume (cubic inches)/10

Thanks!! That's great, I assumed there woukd be a correlation but thought it might not be available as formula.
Thanks again!

Suspicion confirmed...40cubic inches (650ml) would mean 4ounces of greens or approx 110 g and I got approx 70 g out (did not weigh them before)

Well I can go to the drawing board

A quick calculation shows me (unless I"m way off) that 20 cm of that duct would make a cylinder containing 3,5 liters or 213 cu inch, leading me to a load of 21 oz or 588 grams...that is IF I can get enough heat into that beat to be roasting quick enough.
Is there also some math for the heat capacity? (Guess variables are Abundant with insulation heat loss etc..) of greens?
My stove has a 3,5 Kwatt capacity which is enough for some serious baking but my gut feeling is that 500 g of greens may be a bit much to heat up fast enough....

Hmmm. I have heard 5,000 btu per lb? Does that make sense?

Most of what I know about building a roaster comes from www.homeroasters.org. If you haven't checked that forum out you really should pop over there.

Bodka Coffee wrote:Hmmm. I have heard 5,000 btu per lb? Does that make sense?

Thanks again!, now that is a quick response!

5000 btu is 1,5 KW, so seems doable as one lb is approx 450 grams, so if I can channel the heat appropriately it is a go

i did have a loom at the forum you mentioned but that was a while ago and I had some difficulty cutting through the information trying to find flavor profiles of the various roasting methods but I will check in again! (Even though I think it should be fairly straight forward from here.

The name is going to be the 'lean bean machine' a purist approach to roasting ( well, that's what I'm aiming at anyway )

Marcelnl wrote:my second roast in a converted Illy can rotated by an electric drill over a stove.
.

I understand the simple approach, but cans may release toxic materials when heated. Why take a chance?

Cheers

Because I can

But seriously, the inside is not coated and I burned any residue off during a test spin before adding any beans.

Today I tasted the espresso, my hair has not turned green since and the taste was actually very good soI'll survive (taste was way beyond my first attempt and probably store worthy)

But I agree cans can be risky when heated.

Hello:

Bodka Coffee wrote:There is a formula for finding your drum size vs load. Let me see if I can find a link.
Found it- Roast size (ounces) = Drum Volume (cubic inches)/10

Interesting ...

At the moment (for the longest while, actually) I am in the process of building a gas fired solid drum roaster.
I decided on the design and general dimensions based on whatever parts/components I could get my hands on to build it with as little lathe and external shop work as possible. (think $$$)

After finding a suitable source for the drum ends (crankshaft pulley halves from a '94 Renault 18) I went for the pulley's 130 mm diametre and decided on a 220 mm length based on the length of a set of gas burners from a discarded on-demand water heater.

But I digress ...

The thing is that the drum's nominal volume is 2920 cc., which work out to be 178,20 cu. in.
According to the formula, the roast size woud be 17,82 oz. which in turn work out to be 505,19 grams.

Why all the fuss, you may ask?
Because the formula is right on the dot. =-D

Happens that once I'd built the drum, I realised that I did not have the slightest clue as to what it's capacity would be.
So to try to get an idea I propped it at 15° and filled it up with greens to a point that seemed safe enough ie: to roast and turn without spilling beans out as the roast progressed.

I then emptied the drum and weighed the beans.
Guess what? The scale read 498 grams.

Thanks a lot, your formula has given me some peace of mind.

Cheers,

CIV

Sounds good! Keep us posted on your roaster.