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Thread: Gas BBQ roaster

  1. #1
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    Gas BBQ roaster

    I'm just beginning to formulate my home made roaster plan, and didn't want to reinvent the wheel so to speak. So anyone else who has done this or has any pointers, feel free to point away!

    My plan is to have a square rod go across my BBQ, supported by two or three bearings. The rods will pass through one or more roasting baskets.

    Baskets:
    There are readily and cheaply available roasting drums available on eBay. 12 dia. x 18 cm which is approx 2 litres.

    Motor:
    I've picked the smaller diametre for the purpose of minimising torque requirements. For the purpose of calculations, let's say we half fill it with coffee: that should be about 750g of coffee (probably get uneven roast, but worst case for calcs).
    The center of mass of a semicircle is 4r/3pi from the center towards the edge, which gives 4x6/9.42477 = 2.54 cm... just less than half way. Assuming somehow the coffee magically sticks in it's semicircle state until it's rotated 90 degrees, that gives a torque requirement of 2.54 x 0.75 = 1.9 kgcm (0.187 Nm)
    The gearhead motor pictured is rated to 2.2 kgcm of torque at 70 rpm.

    Square rod is just 1/4" or 6.35mm. I have failed to find a square bearing that size, so I will buy a 8mm dia. bearing and take 0.5mm notches out of the corners to fit onto the 6mm square rod (9mm hypotenuse).

    Bearings will mount on the edge of the BBQ and be held in location with small screw clamps to stop everything sliding up and down.

    So the plan is to have one basket full of 750g, or two baskets with 750g between them. The calculation for 1/4 volume full is quite a bit harder, but comes out roughly at 1.54 kgcm, so the motor could have issues with two baskets, but at that stage I'd grab a larger DC motor perhaps with PWM control, also fairly cheap. Worst case I think it'd cost about $100.

    Any thoughts?
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  2. #2
    Senior Member WhatEverBeansNecessary's Avatar
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    What I would recommend is thinking about how you can try to measure the temperature of the beans during hte roast. Once you have found a nice roast method you will want to replicate it as best as possible - i think that might be hard on a BBQ. However with a bean temp probe it should be a lot more straight forward and it should be easier to install now during the design phase than later as an after throught.

  3. #3
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    Thanks, that's a good point. I've been roasting on a popper for 10 years (the same popper!), and its luck will run out one day. I don't measure the temperature or profile, but you get a feel after a while of how fast it's progressing. The popper roasts really well when it's not too hot, ideally below 20 ambient. The colder the better. On hot days I don't roast. The point is I don't currently measure temp, but for larger quantity I image its more important.
    Just having a quick look, getting slip rings won't be hard, the 1/4" shaft will go through most rings and I have some good probes. My main concern is the chaff burning will make the coffee taste smokey / burnt...

  4. #4
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    What about some co2 jets to cool the beans fast?

    Im not a roaster, but from reading here and there its important to be able to get the beans out and cooler, quickly.

  5. #5
    Senior Member fatboy_1999's Avatar
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    Gas BBQ roaster

    I have been using the BBQ drum method for the last 10+ years.
    Very happy with it.
    Yes, the temp probe issue is real. Best I could do was monitor ambient temp inside the roast area but not the bean mass. However, it's not a deal breaker for me.

    The ideas regarding the motor, the rod etc. all seem sound to me.
    I have attached my setup in a word document.

    As for cooling the beans, I have built a couple of bean coolers using PVC storage buckets, extractor fans and sieves. They do the job for me. Others have built coolers using leaf blowers and vacuum cleaners. Have a search of the forum.
    Commercial cooling trays suck air down, but their fans are much more powerful and they have got rid of a lot more chaff during the roast than I can, so I find that blowing the air up through the beans is better for my purposes.

    Good luck. Takes notes. Be mindful of the thermal mass. Bigger roasts can run away from you if you're not careful.

    Brett.
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  6. #6
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    Wow, thanks Fatboy. That's awesome. I lolled at the 'them bones' style. I looked into the eBay drums more and it seems 'stainless steel' doesn't mean much, so I'll likely make my own or just buy a drum locally.

  7. #7
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    I've spent a few weeks looking for scrap to make a BBQ roaster. the company in the US that make stainless drums look great, but that is a more expensive option.
    I've trawled the net looking for food grade stainless drums in about 18" X 8" in the right thickness and found nothing.
    I'm going to start a build thread soon, will need a lot of advice on motor wiring etc.

  8. #8
    Senior Member Beanz.'s Avatar
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    Not sure if you have looked at the Auspit drums. Provided you are not roasting small beans like Yemen this should save a lot of effort. Aussie made and good quality

    Auspit Spit Mate Junior - 24cm | Auspit

    Auspit Spit Mate Medium - 40cm | Auspit

  9. #9
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    Quote Originally Posted by Beanz. View Post
    Not sure if you have looked at the Auspit drums. Provided you are not roasting small beans like Yemen this should save a lot of effort. Aussie made and good quality

    Auspit Spit Mate Junior - 24cm | Auspit

    Auspit Spit Mate Medium - 40cm | Auspit
    Hi Beanz,

    That's the best drum i've seen so far. A little small on the diameter but a good length. Any idea what amount of green beans you can fit in the larger model?

  10. #10
    Senior Member fatboy_1999's Avatar
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    Behmor Coffee Roaster
    They look interesting, but I would be concerned about the load/unload method. Looks like you need to remove an end cap. This would be problematic for roasts as you often need to get the beans out and cooling very quickly.
    If they had a hinged latch on the end or a sliding panel, I'd be on one like me on a pizza!

    Brett.

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