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Thread: My failed simulated corretto

  1. #1
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    My failed simulated corretto

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Just thought Id get my latest failure off my chest, and maybe get some others thoughts on temperature measurement and paddle issues.

    Ive been roasting for a while with a simple heat gun and bowl setup, as shown in the first photo. It worked very well, except for unstable temperature readings - temps jumping up and down according to how I stirred the beans, and how often the probe was briefly exposed to a direct heat gun blast, or an ambient wind gust. FC and SC temps varied too - one day FC would occur at 185, the next day at 165, or so the reading said. In the end I didnt put much trust in the temps, and got good results based on gun height and the feel of it. But I thought ... there must be a better way.



    Unable to find a 2nd hand breadmaker that didnt need modding, I had an idea ... for coffee roasting purposes, isnt a breadmaker just a tall tin with a motorised paddle? Couldnt I achieve the same function with a stainless steel biscuit tin, a motor from Jaycar, and a home-made paddle? The following photos shows the result, where it differs from my previous setup (with closer view of paddle and probe, minus tin).



    The tin has two holes in its bottom - the temp probe sticks up through one at the edge, and the motor axle sticks up through the centre. The scrap metal paddle sits snugly on the axle, but easily comes off when the tin is lifted upwards at the end of the roast. The geared motor axle spins at 12 rpm with enough torque to stir lots of beans ... perfect, I thought.

    Maybe the higher tin would keep outside wind gusts away from the beans, and together with the deeper and more evenly stirred bean mass it would lead to more reliable temp readings. And I wouldnt have to stir with a wooden spoon! I was feeling pleased with myself and my "simulated corretto" ... until I used it.

    Ive just produced my most uneven roast ever. The paddle seemed to stir well, yet some beans still looked green while others were at CS7. Some were still starting FC when others were well into rolling SC, a few on the brink of burning. Even after removing all the charcoal beans, the rest ranged from pale CS5 to dark CS11. Sure, the temp readings were more stable, but no more accurate than before (FC at 160?).

    So not all progress is forwards. Im now thinking what I could change, or whether to go back to the bowl and wooden spoon, and Im wondering:

    * Has anyone else had problems with temperature readings varying due to factors other than the actual bean temperatures?
    * Do you need a certain minimum bean depth to get an accurate temperature? (I roast no more than 230g at a time - my weekly consumption - but I know others roast much more in corretos)
    * Does the paddle need to be a particular shape/size/angle to get thorough mixing? (The breadmaker paddles Ive seen were basically flat rectangular surfaces, like my home-made paddle)

    On the bright side, if someone wants a strikingly mottled roast with raw notes and carbon aftertaste, I can produce one!

  2. #2
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    Re: My failed simulated corretto

    Oops - I forgot to mention in the above post what I was roasting.

    It was a pre-roast blend of Harrar Longberry and Brazil Monte Carmelo, roasted slowly: 12 mins to FC. I know, I should have stuck to one bean while testing a new setup, but Ive roasted those two together before (in the bowl with spoon), for similar times, and they always roasted together very evenly.

  3. #3
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    Re: My failed simulated corretto

    Gday Oily,

    Quote Originally Posted by Oily link=1216996427/0#0 date=1216996427
    * Has anyone else had problems with temperature readings varying due to factors other than the actual bean temperatures?
    * Do you need a certain minimum bean depth to get an accurate temperature? *(I roast no more than 230g at a time - my weekly consumption - but I know others roast much more in corretos)
    * Does the paddle need to be a particular shape/size/angle to get thorough mixing? *(The breadmaker paddles Ive seen were basically flat rectangular surfaces, like my home-made paddle)
    Yes, Yes, and probably not. Now to elaborate...

    Yes, weve had a lot of trouble with temp readings fluctuating 5-10ēC in any 5 second period. We use a K-type (wire) thermocouple and hang it into the bread pan just at the level of the beans. As its not IN the beans, the measured temp is probably more to do with air temp (which would fluctuate that much). Still, we can generally guess at a "5-10 second average" temp and have some idea of where its at.

    Mal suggested (in another thread) that you need a minimum load equal to 40% of your bread pans volume. For most bread pans, this is probably 300-400g minimum (green). Your pan looks significantly bigger than a bread pan and - even though that "ballpark" rule probably doesnt apply - I think youll need more than 230g to get an even roast. Having more beans means that there are more of them to soak up the heat, and more neighbours for each bean to bump into and share heat. Either roast more (double batch every two weeks?) or get a smaller pan, I reckon.

    I dont think your paddle design is flawed (though it would be nice to see it in action... YouTube?) BUT, I would guess that 12rpm is too slow. My breadmaker runs at somewhere between 60-120 rpm (complete guess). Here is a YouTube clip of our roaster in action (http://www.youtube.com/watch?v=7vp8uDws0-8)- feel free to time our BMs rpms... Im on dial-up and cant be bother waiting 10 minute for it to load today. :P So is there any way to gear/power-up your motor to run at a higher rpm?

    Hope that helps
    Cheers,
    Stuart.

  4. #4
    ev
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    Re: My failed simulated corretto

    Id have to sgree with Staurt regarding the bean quantity & size of pan. My BM has a reasonably smallish pan (like most) & I roast 400 or 500g lots. I have the heat probe inserted through the side of the pan buried in the middle of the beans. This set up seems to work well. Try a larger batch & see how you go. Roast enough for 2 weeks. In my experience, Ive found that they last quite well as long as I dont over roast.

    Evan.

  5. #5
    Senior Member Koffee_Kosmo's Avatar
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    Re: My failed simulated corretto

    Jaycar has a motor
    Part # YG2734
    12 Volt
    36 RPM
    Max weight it can push is 12 KG
    Cost $19 to $20

    This set up is similar to CS member Martybean

    KK

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    Re: My failed simulated corretto

    Thanks guys,

    I found the thread where Mal wrote about bean load v. pan volume, and it makes sense. A bigger load would also cover the probe more effectively. Also watched Stuarts youtube video - if a picture is worth 1000 words, a video like this is worth a lot more! I didnt time the paddle, but it was whizzing around heaps faster than mine.

    By the way, the motor Im using is the one quoted by Koffee Kosmo, so its 36 rpm not the 12 I stated (the volts and torque are both 12 ... i must have confused them). Even so, I suspect its slow speed relative to the breadmaker could be a big part of the problem. Ive roasted 230g batches nice and evenly in my large bowl - but with very vigorous and very thorough (not to mention laborious) stirring with the wooden spoon. This manual stirring far exceeds what the 36rpm paddle does.

    Im thinking that 230g might be evenly roastable in the biscuit tin if I can get the paddle to rotate considerably faster, which Ill have a go at next. But i need a coffee first.

  7. #7
    Mal Dimal's Avatar
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    Re: My failed simulated corretto

    Quote Originally Posted by Oily link=1216996427/0#5 date=1217040435
    Even so, I suspect its slow speed relative to the breadmaker could be a big part of the problem. Ive roasted 230g batches nice and evenly in my large bowl - but with very vigorous and very thorough (not to mention laborious) stirring with the wooden spoon. This manual stirring far exceeds what the 36rpm paddle does.
    Gday Oily,

    Another way to overcome the speed of agitation problem, is to add more stirring vanes to your existing setup; probably at 90 deg. to each other. This would have the effect of stirring at twice the speed and if that little motor is able to produce torque within the 12Kg region, it should be well up to the task.

    If you do decide to give this option a go, rather than make the new vanes exactly the same as the originals, try making them a bit shorter and maybe with a slight scooping action towards the tip. This should pick up any beans that might be circulating around on the bottom of the pan. I guess its just a matter of trial and error to see what sort of action produces the most thorough agitation.

    Cheers mate,
    Mal.

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    Re: My failed simulated corretto

    Just a thought.
    BM bins are square or rectangular. ie. have corners which disturb the flow of the beans and maybe give a better mix.
    Maybe with a round bin you dont get this mixing action. The beans just go around and around.
    Might explain the uneven roast.

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    Re: My failed simulated corretto

    Hi there. I have just done something quite similar but with a turbo oven. (http://coffeesnobs.com.au/YaBB.pl?num=1211421295/20#20). I used a jaycar motor with 2 arms to agitate. It happily does 500gms, and the roast comes out very even. I am wondering with your design if you would get lots of beans on the outer edges that are not stirred, as you shortened the arm to allow for the thermocouple? But this may be where my design differs from yours - the air from the oven on mine will not move the beans at all, whereas I gather the heat guns give considerable movement.

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    Re: My failed simulated corretto

    Hi Oily, before i made my corretto just recenlty.I had something like your roaster and I found that if I chocked up one side of my pot that when the stirrer came around it picked up some beans and the others fell back to the low side.This method worked really well .You might find that as I did the last gear on the motor keeps on braking off I used 4 motors untill I made mw corretto but good luck anyways.
    Marty

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    Re: My failed simulated corretto

    Hi Marty, interesting to know about the your motor failures. If I get a failure like you describe sounds like I will ahve to redesign rather than replace. Im only about 5 roasts in with mine, and all ok so far!

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    Re: My failed simulated corretto

    Hi all Im new to this game after bieng introduced to espresso a month ago and struggling to get a good shot out of a Krupps with pre ground beans. Trying to convince the wife that I need a new machine and an expensive grinder without much success so will probably head down the second hand path from a charitable CSer with any luck.

    The roasting has caught my attention and have been reading forums and noticed this thread. I have a bread oven, turbo oven and popcorn maker. I was thinking that a mod taking the motor from the bread maker onto a frypan and then using the turbo oven would be a good way to go.

    Any thoughts?
    Do the heat guns pack it in relatively quickly?

  13. #13
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    Re: My failed simulated corretto

    Aha! More good ideas.

    As Mal suggests, I could add more stirring vanes. Damian is correct in that I shortened the single vane to allow for the thermocouple, so another vane which sweeps right to the edge ought to help (I can move the thermocouple elsewhere). Raising one side of the tin to introduce some irregularity, as suggested by Martybean, also sounds well worth trying.

    I appreciate these ideas - having been so focussed on a method I thought would work, changing my mindset hasnt been easy, especially after the discouragement of a bad roast. My simulated corretto may yet succeed! I wont get to try any changes for a little while, but will report how it goes.

    Do the heat guns pack it in relatively quickly?
    antc:
    The important thing is to blow a fan at the guns air intake while in use to avoid premature burnout. With this, a decent gun should last well. I use a Ryobi EHG2002 (about $46 in Bunnings) which seems well regarded by other CS members, and I think someone (i forget who) has had 70+ roasts from that model. Another member got 150 roasts from a Ryobi, not sure which model. This thread has a lot of info on heat guns:
    http://coffeesnobs.com.au/YaBB.pl?num=1176799309/0

  14. #14
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    Re: My failed simulated corretto

    Quote Originally Posted by antc link=1216996427/0#11 date=1217083332
    Hi all Im new to this game after bieng introduced to espresso a month ago and struggling to get a good shot out of a Krupps with pre ground beans. Trying to convince the wife that I need a new machine and an expensive grinder without much success so will probably head down the second hand path from a charitable CSer with any luck.

    The roasting has caught my attention and have been reading forums and noticed this thread. I have a bread oven, turbo oven and popcorn maker. I was thinking that a mod taking the motor from the bread maker onto a frypan and then using the turbo oven would be a good way to go.

    Any thoughts?
    Do the heat guns pack it in relatively quickly?
    Welcome antc.

    Dont buthcher the breadmaker AND the turbo oven.

    Do a search for "corretto" and youll see its easy to use or convert a breadmaker to roast coffee.

  15. #15
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    Re: My failed simulated corretto

    Behmor Coffee Roaster
    Quote Originally Posted by antc link=1216996427/0#11 date=1217083332
    I was thinking that a mod taking the motor from the bread maker onto a frypan and then using the turbo oven would be a good way to go.
    Yep. Many people have made similar roasters using turbo ovens. Do a search and youll find many ideas out there on the net.



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