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Idea for halogen roaster
Danyboy
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Posted on 11/15/2017 7:05 AM
Hi guys,
New to the forums here, but been reading as many threads as possible. I wanted some input as to whether the following idea would be workable based on your collective experiences, prior to embarking on a potentially dead end journey. I would like to roast 300-500g of coffee.

What I'd like to build is a halogen roaster that would resemble a Behmor. I would use an old toaster oven as the casing (would gut the electronics), and put in a mesh drum (the $10 ones on ebay) attached to a 30ish rpm worm drive motor.

As a heat source, I was thinking of attaching 2-3 halogen bulbs between 700-1000 watts each (2 x 1000 or 3 x 700) to the inner walls of the oven, at an appropriate distance from the drum, maybe ~3cm. The advantage of having multiple bulbs would be to have some degree of control over temperature. They are also very cheap ($3 on ebay for 1000W lamp)

What I was more worried about were the following:
1. Air flow - would there be any advantage to having a fan to circulate air within the oven? I was thinking about having a closed air circulation circuit (using ducting) with the possibility of a vortex for chaff collection. The advantages of the closed circuit would be less heat loss and possibly additional heat delivered to the beans for drying/roasting. My main concern would be finding a fan that can function when subjected to the temperatures of a roasting chamber.

2. Cooling - There would be no easy bean dump due to the form factor. Instead I was thinking of the above concept of air circuilation with the option of having the air intake from outside the oven instead of recircuilating (either by having a mobile port to switch the air intake from inside to outside). OBviously would need to be a powerful enough fan - eyeing fans with a cfm > 500

3. Heating - the alternative to 2-3 halogens would be to have something like a ceramic heater for IR + a halogen lamp.

Would anyone care to give me some feedback as to whether they see any obvious problems, or whether similar projects in the past have failed/succeeded? I've read through some of the threads describing halogen ovens that people have built, but unsure how that would relate to my design idea...
 
renatoa
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Posted on 11/15/2017 7:33 AM
Used for some 6 months a similar approach, i.e. drum in an enclosure, and abandoned due to the hassle of loading and dumping beans = handling of a hot potato... er. drum smile
Also, measurements inside a drum aren't that simple.
Other notices:
- power is over-estimated, 1kW is enough for 500 grams. I am roasting atm up to 650 grams using 1400 W, that are fully used only 2-3 minutes in the dry phase, then power is reduced to less than 1kW, even less than 500W in development phase.
- airflow is a must ! using a turbo oven lid, that includes a turbo fan, is the simplest and cheapest solution. Else chaff will stay in the drum and burn => smoked coffee.
- cooling is indeed difficult for drum approach, but much easier when using a flat pot with rotating agitator, like stir crazy. You simply remove the halogen lid and place a fan of same size above the beans, no more need for dump until beans cold.

A solid drum approach with halogen inside, that broke my jaw, not so difficult to replicate, can be found here:
http://www.dbr.co.nz/radiant.html
The build has a thread somewhere here, with some additional explanations that were asked by users.

Or, if still loving the behmor style of roasting, evaluate using a George Foreman ove, seems the most appropriate for such task, with some success stories around.
Still many issues to solve even for GF approach: faster drum turn, chaff management, airflow...
Roasters: DIY: TO based IR 200-640g
Commercial, moded: Skywalker, Dieckmann RoestMeister, Nesco, popper(s).
Electronics: TC4ESP (author), MS6514, USB/Artisan/Apps (contributor), PID controllers
Grinders: Potu ghost burrs, Arco, Xeoleo ghost burrs, Krinder, vintage PeDe Dienes, MBK Feldgrind, Kinu M38
Brew/presso: ALM pour over, Arin lever, Staresso Mirage, Hario Cafeor dripper, Flair Signature, Kompresso, Aeropress, Gaggia Mini
 
renatoa
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Posted on 11/16/2017 3:02 AM
A second read notice, 3 cm from the drum is too close, could heat the metal more than 300C => beans scorching/tipping.
Several sources points that the shortest safe distance for direct to bean heating is 3"/8 cm.
 
Danyboy
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Posted on 11/16/2017 6:35 PM
Hmm thanks
Good to know
8cm - will need to get a large enough toaster oven and figure out how much volume the bean mass occupies to get the dimensions right
Will definitely try for a solution with air flow. Wondering if there are any fans that can handle the heat...
 
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