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Thread: Uneven roast - coretto setup?

  1. #1
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    Uneven roast - coretto setup?

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    On Sat. I roasted 600g (500g post roast) of Uganda Kisoro to about CS8 (it's a little darker than it looks in the photo).
    I always point the heatgun onto the wall of the mixing tin above the beans and not directly onto the beans themselves.
    In general the roast was quite uniform but with a small percentage of over roasted beans to CS12+.
    I manually sorted these out and ended up with about 1% of unusable beans - no big deal.

    I know it is not this particular bean as all my last batches have shown the same amount of burnt beans.
    I have been trying different gun positions and bean quantities but with the same result.
    From memory I don't think I used to get an uneven roast at all - but I can't be sure.
    I am just wondering if this is typical for a Coretto roast or I should continue trying different arrangements.


    Uganda_Kisoro.jpg

  2. #2
    Life-long Learner DesigningByCoffee's Avatar
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    I think they certainly looks like scorched beans, which would indicate that perhaps the tip of the gun is too close to the bean mass or the gun is too powerful/hot. What is your setup? Any photos?

    I roast 750-800g batches in a standard sort of pan, but have it lidded and well insulated, and a chimney that the gun goes into which keeps the tip at least 80mm + from the bean mass at all time (variation occurs due to the bean mass expanding as you roast and they get closer to the top of the pan).

    FWIW a lid and insulation is the biggest benefit I reckon - they allows you to drop your gun temperature substantially (is you gun heat adjustable?) to give the same profile with far less direct heat input, greatly reducing the possibility of scorching (I've never even seen scorching in 200+kg of corretto roasting - lots of other faults - just not that one! ).

    That is where I'd start

    Cheers Matt




  3. #3
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    It could be that some of the beans are not being moved around, due to insufficient bean agitation. I had this problem a while back with my current corretto setup and I resolved it by extending the BM's mixing palette, making it from an L profile into an ╩ . To do that I used a piece of strong wire that I epoxied to the palette to extend towards the back. That solved my problem perfectly.
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  4. #4
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    All good suggestions. Thanks.
    I particularly like your setup Matt. Unfortunately I don't have a variable temperature heatgun and can't reduce the heat output.

    Now that you've confirmed there is an issue I think I've found my problem.
    I uncovered my old roast logs (which I thought were lost) and it turns out I was only roasting 500g at a time.
    With the larger quantity of beans I am doing now, the bean mass sits higher in the tin and I guess some are being exposed to the direct heat from the gun.
    I did try adjusting amounts but obviously not enough.

  5. #5
    Senior Member noonar's Avatar
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    A modified extension nozzle on the end of the heat gun also helps to keep the beans away from the direct heat of the gun which I did before I acquired a temp adjustable one. It works well controlling temperature. Another heat control mod is to make a heat diffuser from an old sieve (no too fine) and fix it in the hole of your roaster lid concaving into the pan of the roaster.
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  6. #6
    Life-long Learner DesigningByCoffee's Avatar
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    All good options above

    The mixing can be an issue - I've modded my paddle as well as the big batches just stopped moving on top late in the roast.

    As proof of concept, if you wrap your pan in a few layers of alfoil, increasing the height of the walls 100mm or so then moving the gun up, that will still contain the heat (it is the airflow that strips off too much heat when the gun goes higher in an open system, then see if the scorching stops and what changes it makes to the profile.

    Just remembered … I have a mesh diffuser inside the chimney too, but mine was to stop beans jumping into my 'heat splitter' at full song…

  7. #7
    Senior Member greenman's Avatar
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    My Mk I Corretto had a Ryobi heat gun without variable temp control. I mounted it on a sliding shaft to slide the gun away from the roast as it progressed, it worked quite efficiently until I got the variable temp and fanspeed heat gun which added a whole new dimension.
    Attached Images Attached Images
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  8. #8
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    My setup looks a lot like greenmans above.
    I'm doing another roast on the weekend and will try some of the suggestions listed.
    I'll probably try raising the tin height with foil first and diffusing the airflow from the gun.

  9. #9
    Senior Member Yelta's Avatar
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    This is my setup, along with a pic of a roast I did some years ago, the roast is typical of what I produce on this Corretto.

    To control airflow I experimented with the size of the exhaust opening during the initial setup many years ago, what you see below works well for me, I seldom experience problems with unevenness.

    The heat gun is a Bosch variable speed fan, probably the most important item in the chain, I run it on medium fan speed , and always feel I'm well in control of the roast.

    The paddle on my single loaf Breville agitates very well, keeps the beans moving nicely.





    DSC_0276_1000x669.jpg
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  10. #10
    Senior Member noonar's Avatar
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    Quote Originally Posted by DesigningByCoffee View Post
    I think they certainly looks like scorched beans, which would indicate that perhaps the tip of the gun is too close to the bean mass or the gun is too powerful/hot. What is your setup? Any photos?

    I roast 750-800g batches in a standard sort of pan, but have it lidded and well insulated, and a chimney that the gun goes into which keeps the tip at least 80mm + from the bean mass at all time (variation occurs due to the bean mass expanding as you roast and they get closer to the top of the pan).

    FWIW a lid and insulation is the biggest benefit I reckon - they allows you to drop your gun temperature substantially (is you gun heat adjustable?) to give the same profile with far less direct heat input, greatly reducing the possibility of scorching (I've never even seen scorching in 200+kg of corretto roasting - lots of other faults - just not that one! ).

    That is where I'd start

    Cheers Matt



    Just a heads up. Aldi have fire blankets for sale at $7.99 (on the WA side o the country at least) for anyone looking for an insulation upgrade option for their bread machine bean roaster.

  11. #11
    Senior Member Magic_Matt's Avatar
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    Behmor Coffee Roaster
    Dang, I nearly bought one the other day! Maybe they'll have some left.



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