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Thread: Stirring beans...

  1. #1
    KJM
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    Stirring beans...

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    My colleague Hazbean suggested I post this.

    I have a home-brew roaster which uses both a turbo oven and an electric frypan as heat sources. It also has a stirrer to keep the beans moving. Somewhat inspired by Farmroast's rather lovely 1kg sized roaster of similar construction, I made my stirring mechanism out of 3mm stainless rod rather than the more usual bent flat section.

    Over the last couple of years of using this setup, I've taken to (manually) turning the stirring off and on in a crude PWM fashion. A couple of weeks back, I decided to automate that and now have the microcontroller doing the PWM of the motor to control how much stirring gets done.

    I operate the stirring arms at a VERY low duty cycle. What I've settled on is basically between 5 and 10 seconds off, and one second on. This results in 100% perfectly uniform roasting with no scorching or tipping.

    The noise from the roaster is now quite tolerable - there are periods of silence. Hearing FC (or second crack) is not an issue at all, and it is overall rather more pleasant to use. I suspect this experience can't be transferred to those with drum style roasters (due to the mechanical arrangement) but for those who have KKTO or similar roasters, this would apply. The only thing is I use a geared 24V motor (running at 12V) for the stirring - so it is quite fast. If your KKTO just gently sweeps the beans, the on-time might need to be increased.

    Anyway - I view this as a useful mod, and will keep doing this. It really makes the roasting experience more pleasant and it seems to have no nett impact on roast quality whatsoever.

    /Kevin

  2. #2
    Life-long Learner DesigningByCoffee's Avatar
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    Hi Kevin
    That sounds really interesting - do you have any pics or vids? I've often wondered about an electric frypan or deep fryer base combined with a T.O - did you just drill through the centre of the frypan for the stirrer?
    (Sorry in advance if all this info is featured somewhere else!)
    Matt

  3. #3
    KJM
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    Well, no piccies till I beautify it a little

    The stirrer mechanism is due for a slight re-engineering. I need to get around to it I drilled a large hole in the centre of the circular frypan - which has an aluminium base (easy) and stainless bottom (not so easy). There is a length of 1/2" running nipple screwed into that and the shaft comes through the middle... It limits the depth of beans you can sensibly put in somewhat, but the thermodynamics of the roaster limit that anyway.

    My frypan was a Sunbeam, and it had a casting dimple in the middle, which made finding the centre pretty straight forward. I've got the thing centred within 10 thou or so - so the stirrer arms are quite happy. My stirrer shaft (at the moment) is nothing more exciting than a 100mm M8 stainless bolt.

    When my round tuit arrives - I'll be reaming the ends of the nipple to take some stainless ball bearing assemblies and the shaft will be supported top and bottom. At present it kind of flails about a bit, but the running nipple is brass, so apart from the noise of the bolt head and welded on arms rubbing, it does little harm. It is also getting nicely polished You always need to look for an up-side to being a lazy arse

    The other issue I have is that the motor mount isn't done right. I had an elaborate plan for making it adjustable in all directions, but when I checked it for fit it was within engineering tolerances of "just fits" - so I TIG'd it in place.

    When you decide to do things like that, it is always better to clamp and check rather than freehand hold I knew that before I did it, but...

    So there are a couple of wee details I need to fix before I publicly show the franken-roaster!

    As a random data point: it roasts 650g (green) batches perfectly. If you go bigger - say 800g - the roast times wind out just a bit. At 1kg, there is a significant stretch in roast times - so the combo is basically a 700g or so job. If you run both the heaters flat out though - you could probably shoe-in 1kg (or more). But that is more than 11amps out of the wall, and the engineer in me says no. So the roast times are limited to the (slightly arbitrary) 1800W limit I've put into the control regime.

    /Kevin

  4. #4
    Life-long Learner DesigningByCoffee's Avatar
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    Sounds like you're having some awesome shed time :-)
    Will follow with development with interest!
    Matt

  5. #5
    KJM
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    Quote Originally Posted by DesigningByCoffee View Post
    Sounds like you're having some awesome shed time :-)
    Will follow with development with interest!
    Matt
    Shed time??!?!? I wish! Keeping the old house from falling apart, the 25 year old Kubota tractor running and roasting coffee! I *really* need that round-tuit!

    The Franken-Roaster is on the list though. S/he (does a roaster have a sex?) needs the insulation re-worked and the chaff exit majorly re-done and the motor/shaft system re-done. All of which will take not that much time, but I do need to find that time...

    Actually roasting coffee is such a distraction

    /Kevin

  6. #6
    Life-long Learner DesigningByCoffee's Avatar
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    Ha Ha!
    I used to be an Industrial Arts teacher, elbow deep in grease & wood shaving. Now I'm a graphic designer in front of a monitor all day - I actually miss all those old machines & tools that need work! (plus all those works shops full of gear ready for 'special orders' on the weekend!)
    Maybe I should borrow the tractor for a fix!

  7. #7
    KJM
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    Behmor Coffee Roaster
    Quote Originally Posted by DesigningByCoffee View Post
    Ha Ha!
    Maybe I should borrow the tractor for a fix!
    As long as it is returned with all the pins and bushes replaced (and reamed) in the front end loader

    But seriously - all of us with horizontal stirring mechanisms can tone down the stirring without worrying about burning/tipping/cratering. It does make the whole process rather more pleasant - which is why I posted the data.

    Cheers
    /Kevin



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