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Thread: 2 burner Barbeque (BBQ) drum roaster build - A documented story

  1. #1
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    2 burner Barbeque (BBQ) drum roaster build - A documented story

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Good afternoon all
    For what seems like an age I have been thinking about building a BBQ roaster (probably since reading about Brett's - Fatboy_1999 - adventures) and procuring a 2 burner BBQ for nix.

    I thought I'd do some documenting so it might help others who are thinking of taking the plunge and it may also gain me some more advice before the construction actually begins which will save some tweaking of the system post build.

    I am lucky enough to have a brother in law who is very handy on the tools and has a great mind for building and designing things that are slightly left of field. I had a concept for what I hoped would work, but he will be the main reason it comes to fruition.

    First off - One of the main considerations for me, was to keep the price as low as possible whilst making a roaster that will produce good results, so most of the parts have been sourced on the cheap. If your budget is larger, then some of this process might be a little easier (and quicker)
    I have attached some pictures to help paint a picture of what we are about to attempt -

    Pic 1 - The BBQ is a 2 burner with a hood
    Pic 2 - The original concept for the roaster
    Pic 3 - The roaster will be 2 stainless steel colander’s bought from Ikea. They will be welded together to form the roasting barrel - the handles will be removed.
    Pic 4 - I bought a small stainless bowl which will have the bottom cut out and be welded to one end of the roaster to act as a funnel instead of having a hatch to open at the end of the roast to dump the beans
    Pic 5 - The motor set up to be used is from a golf buggy and has a variable speed function so we can adjust the RPM of the barrel

    We will reinforce one of the ends of the barrel and have a piece of stainless rod running through the centre. There will also be a piece of stainless towards the other end of the barrel welded in, so the rod can pass through another point for extra support.
    The plan is to have 2 vanes of stainless angle iron running down the length of the barrel at a slight angle so that the beans are agitated during the roasting process
    We will also build a table for the whole set up so that the motor/BBQ/bean cooler will be integrated and can be moved around easily. We are hoping to design the roaster so that it is hinged in a way that once the roast is complete, the roasting rod will disengage from the motor and be tipped straight into the bean cooler (via a hinge mechanism) to negate the need for gloves or moving the roasting drum in any large way to get to the bean cooler.

    In another thread about batch sizes for the drum (Batch sizes for a drum roaster) it was suggested that we should add some sort of extraction for smoke so that it is not trapped under the hood during roasting and therefore tainting the flavour of the beans. I would value any advice other BBQ roasters might have regarding their extraction set up if any.

    My initial thoughts would be to cut a hole in the top of the hood and run some ducting to a thermo fan that I have for my bean cooler. The ever willing to help – Mal – let me know that it would be good to have the air flow run bottom to top, which suits my original thoughts.
    I plan on doing a bit more research on this, but would the heat loss from the smoke extraction be a factor at all in the roasting process?
    I think that is all for the moment. I will be talking to my brother in law this arvo to nut out more of the design and we hope to begin the actual build in the near future depending on spare time available.

    I am happy for any questions/comments/accusations that are relevant to the build and I hope to keep the thread updated as we go.
    Cheers
    Shannon.
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  2. #2
    Mal Dimal's Avatar
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    G'day again Shannon...

    Yes mate it will have an effect but probably nothing disastrous so long as your "thermofan" doesn't draw huge amounts of air through. You will most likely, only have to run the fan at low speed initially, say after 120C up to 170C, then maybe a little more from that point onwards. Only really need enough to clear out the smoke and if you think you may also want to capture or remove chaff, then a little more for that. Given that there will be a lot of unknowns in your initial and unique setup, there will have to be a fair bit of trial and error to establish just what is going to work, as intended.

    Should be a lot of fun though...

    Mal.
    P.S.
    Out of interest, what is the diameter of the holes in the Colander/Drum setup?
    If too small, it may not be possible for all of the chaff to escape and be removed...

  3. #3
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    Hi Mal, thanks again for the feedback
    I will need to look at the thermo fan to see if I can put a variable speed controller onto it. I think given its original purpose (cooling my 354 Hemi) it may be a little too powerful at full speed

    As to the size of the holes in the colander - they appear to be 4mm.

    If this is not adequate to allow chaff to escape, we can change the design. I have a metal fabrication shop just down the road that have said they can do something for me, it was just these came in at $9 each so was a good option to keep costs down and was an almost perfect fit out of the box for the BBQ.
    With all the work that will go into this though, I want to make sure we don't let ourselves down at the start by creating a barrel not fit for purpose.
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  4. #4
    Mal Dimal's Avatar
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    Ah yes, I think the Hemi Thermofan will definitely be over-kill...
    Probably try and source a fan that can be driven externally from the airflow, because of the temperatures involved - A small centrifugal fan such as those used in a myriad of automotive air-cons, heater demister setups which would be able to be driven by a variable DC supply...

    See how the drum hole size goes once you start using it, 4mm may be fine.

    Mal.

  5. #5
    Senior Member Lyrebird's Avatar
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    You could try a convection oven fan and add a cowling. They are designed to be used with the fan motor mounted outboard of the heat, I did this for the air distribution fan in my composites curing oven and it works well (but I don't need variable speed).
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  6. #6
    Mal Dimal's Avatar
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    Excellent suggestion Lb...

    Mal.

  7. #7
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    Hey mate,
    Had the same thought as you for the past 10 or so years. Over the last 9 months I actually made it.
    I've got a thread here that I'll update soon.
    Mine is far from engineered properly but a test roast worked (patchy). I've since added a variable speed controller for the motor.
    Total cost about $50.
    Only thing I will upgrade in the future is the drum.
    cheers.
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    Thanks BOOsting
    I had read your post regarding your build. I will be excited to see the finished product, and to see which drum you endied up choosing. Did you put any exhaust fan on the system for smoke?

    Mal / others - I've been thinking about the exhaust side of things and saw on another forum (Homeorasters) that another had cut a 4 inch hole in the hood and put ducting with an inline fan, which was pretty much what I had been thinking.
    A thought came to me that would it be enough to simply cut the hole and put a short chimney on top - without the need for an actual extraction fan - like a flue in an open fire place? I understand if we have forced extraction it could be of benefit if we needed to clear the smoke quickly, but want to be sure we need it before spending the $$ on a luxury.If it benefits though we are very willing to incorporate it into the build.

    *we are also thinking of creating a slide hatch to cover the exhaust hole, sort of like in the grinder to lock the hopper off from the throat of the grinder so that it can be closed whilst getting the BBQ up to temp and maybe at certain times during the roast

  9. #9
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    Thanks LB, good thinking, they are built for this sort of thing and could be sourced cheaply and easily I reckon.

  10. #10
    Mal Dimal's Avatar
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    Well, I guess you could try with just a chimney/flu setup and see how that works for you.

    My take on it though, is that you don't want smoke to build up what so ever, otherwise you will probably be able to detect it in the cup. Maybe you will like it, maybe not and then you could fit an extraction fan. Don't know about an inline fan though, would want to be capable of handling temperatures that would cause most plastics to off-gas substantially, at the very least and maybe start melting...

    Mal.

  11. #11
    Senior Member fatboy_1999's Avatar
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    Shannon, I got your PM but due to a weird error related to me being around so long, I cannot reply to PM's.

    I'll do my best to answer you here.

    I run a 4 burner BBQ that does not actually form a complete seal when the lid is shut. EG: There is a gap for heat and smoke to escape.
    With that in mind, I have never felt the need to implement any sort of flue or fan.
    I roast nearly 2kg at a time and the smoke is certainly noticeable during the roast, but I cannot say that I particularly taste it in the cup.
    Who knows, perhaps it is a little smoky, but since I've been doing it this way for 14 years, I'm just used to it.

    What sort of volume are you looking to roast at a time?

    The other question for you: How will you be dumping/cooling the roast? Arresting the roast is critical especially when roasting outdoors on a hot day. You can go from pulling the roast before 2nd crack to a rolling 2nd +20 pretty quickly without a good cooling setup.

    Hope that helps.

    Brett.
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    Hi Brett
    Thank you for getting back to me. I remember hearing about the PM issue, but didn't realise it was still affecting people.
    Good to know about how your set up deals with the smoke. Originally we were looking to try and seal the BBQ as best we could to alleviate heat loss, which pretty much means a flu is a must. We might toy with the idea of not sealing the BBQ/hood up initially and see how much smoke escapes before cutting into the hood. I'll mull that one over. My BIL has let me know he has a small fan from a fan forced oven that we can use, so we have the ability to put a flu in cheaply as well.
    I am hoping to roast around 1kg batches (I have always wondered - is there a limit on how many beans can go into the roaster before it becomes ineffective?)

    For bean cooling - we are integrating a 20L bucket into the BBQ trolley that will have a thermo fan in the bottom of it. We are designing the roaster to be hinged so that once the roast is completed, we simply lift the hood and the roaster will lift up and pour straight into the bean cooler. I will post some design and build pictures hopefully soon as our roaster design has changed slightly from the original so it is easier to run the roast and dump the beans a little easier and without the need to touch any hot surfaces.

    I do have a further questions about the vanes inside the roaster - do they have to protrude through the bean mass?
    For example when the beans are loaded, they fill the bottom third of the roaster - do the vanes need to come up to a third of the hieght also for sufficient agitation, or can they remain at say 10 - 20 mm and that is sufficient to keep all beans moving how they should?

  13. #13
    Senior Member fatboy_1999's Avatar
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    The vanes on mine are quite large. Probably around 50mm.
    I bought this from RK drums in the US.
    As to whether they are needed... I would think their design has evolved according to their experience over the years.
    Having said that, do the larger drum roasters have vanes inside at all?
    20190406_142206.jpg

  14. #14
    Mal Dimal's Avatar
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    Behmor Coffee Roaster
    Quote Originally Posted by fatboy_1999 View Post
    Having said that, do the larger drum roasters have vanes inside at all?
    Petty sure they do but they're not called vanes, but Lifters as in lifting the beans from the bottom of the drum...

    Mal.



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