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Thread: Roasting with a K-Mart convection oven

  1. #1
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    Roasting with a K-Mart convection oven

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hi guys, today I started my first coffee roasting attempt. I used a K-mart convection oven with a rotisserie and brought a stainless mesh drum from ebay. The first one seemed to come out the best. I turned the top and bottom elements on full and turned the rotisserie on.

    The beans hit first crack at around 10 minutes. At about 15 mins I hit second crack and I then took the basket out of the oven and tipped them into a colander to cool. The problem was though I didnt realise the second crack was actually that.

    So my 2nd and 3rd attempt I was waiting for more than just one crack to signify first crack and burnt the crap out of them and they ended up charred and black. I didnt realise until afterwards that first crack meant the very first time you heard a crack. I thought all the beans had their first crack, then it stops then awhile later they have a second crack.

    I now realise that the first crack you hear is first crack. So my 4th and 5th attempts turned out really well and Im looking forward to trying it out.


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  2. #2
    Senior Member Jackster's Avatar
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    Haha, how good is that!
    I see catch sell one similar with a rotiserie also. Its $113.
    (Kmart one is $100)...
    Would it need to spin a bit faster?
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    Well I wondered about that. It probably should spin faster and I might see if I can tinker with it to do so, but it seemed to turn out ok at its current speed.

  4. #4
    CoffeeSnobs Owner Andy's Avatar
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    Quote Originally Posted by Truman49 View Post
    Hi guys, today I started my first coffee roasting attempt.
    Fun times!

    So my 2nd and 3rd attempt I was waiting for more than just one crack to signify first crack and burnt the crap out of them and they ended up charred and black. I didnt realise until afterwards that first crack meant the very first time you heard a crack. I thought all the beans had their first crack, then it stops then awhile later they have a second crack.
    Your initial thought was right.

    In perfect circumstances all the beans will crack at once, there are always few that crack earlier but as a rule, they will all crack at around 196C. This is an internal crack inside the bean and can be similar to popcorn popping.

    Sometime after that (if you are planning on roasting that dark) there is a second crack which is external to the bean, often it's seen as fracture on the flat side of the bean but is far more subtle, think cellophane rustling.

    I can see at least one divot in the picture, that's where the pressure in the bean blows the back of it off. That might be what you confused 2nd crack with.

    Play around with your weight of beans to try and roast a little slower to 1st crack and the divots should go away, you should also get a more even roast.

    The times above make it sound like the toaster ovens are far more powerful then when I fiddled with one.

    Took me a while to find the thread but 14.5 years ago (wow! 14.5 YEARS) I had a reasonably successful play with an Aldi toaster oven
    https://coffeesnobs.com.au/roasters/...otisserie.html

    It didn't produce enough heat to roast (it baked) but it was improved by moving one of the elements to the bottom and later improved by making my own gas burners for it.

    You might not have to go that far but keep playing, it looks like you are on the right track.
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    Quote Originally Posted by Andy View Post
    Fun times!



    Your initial thought was right.

    In perfect circumstances all the beans will crack at once, there are always few that crack earlier but as a rule, they will all crack at around 196C. This is an internal crack inside the bean and can be similar to popcorn popping.

    Sometime after that (if you are planning on roasting that dark) there is a second crack which is external to the bean, often it's seen as fracture on the flat side of the bean but is far more subtle, think cellophane rustling.

    I can see at least one divot in the picture, that's where the pressure in the bean blows the back of it off. That might be what you confused 2nd crack with.
    Ok well at about the 10 min mark I heard one crack. Then at around 12-14 mins I heard a lot of cracks. At least 10 in 10 second. The first time I thought this was most of the beans going through first crack so I waited for second crack. But by 15-18 min they had turned to charcoal without ever producing a second crack. So I thought first crack must mean the very first time I heard a pop. Then when I heard many cracks a few minutes later I thought that must be s3cond crack.

    So why m I not teaching second crack then and the beans are turning to charcoal before I do?

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    After reading your 14.5 year old thread Andy I had another go tonight and this time used 1/2 a cup (100 grams) instead of a full cup. Here are my results. (Keep in mind Im using a meat thermometer wedged along the side wall and resting in the rotisserie bracket.

    * Beans in at 160C

    * 5 mins = 178C

    *7.47 mins = 1 first crack

    *8.20 mins = lots of multiple cracks

    *10 mins= 2nd crack, smoke starting to come out

    *11 mins = beans pulled put to cool.

    2nd attempt. 100 grams beans

    *beans into cool oven 40C

    *5.23 mins-= 173C

    *7.00 mins= 181C

    *8:13 1 crack 181C

    *9.27 mins=a few more single cracks

    *10.30 mins= lots of cracks (signifying 1st crack) 180C

    *13.10 mins= 2nd crack, pulled beans straight away.

    Heres a photo of what they looked like.


    So does it matter that Im not getting anywhere near 200C or higher as ling as Im getting second crack?

    Why is it that with 250 grams I dont seem to get to second crack without burning them but I can with only 100 grams?

    Is it worth disabling the thermostat to get higher temps? I could here it cutting in and out even when set to full? (NB, Ive built guitar tube amps from scratch that have 350-400VDC inside and fancy 4V brew rig controllers so know my way around electronic devices enough to be careful)

    What bout moving the elements like you did in your build?
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    CoffeeSnobs Owner Andy's Avatar
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    Way too many questions in there to answer without sending you a consulting invoice!

    1: Don't get hung up on numbers, they are just numbers and every roaster is different. Results are what you are chasing.
    2: This is much prettier roast and far more even. You are close to the "right" bean volume I think.
    3: The bigger volume will have less agitation = more uneven it will also roast differently (which you also found).
    4: You are certainly in second crack (I can see them) and still have some divots so potentially still a little fast or hot towards the end of the roast.
    5: I wouldn't fiddle with that toaster oven, it roasts coffee (unlike my Mezzo which didn't have the punch out of the box).

    I would also suggest that you don't have to hit second crack to produce great drinking coffee, if you can get consistent enough then cooling before second crack starts might produce nicer coffee. ...but as a home roaster, you should aim to roast to suit your own taste.

    Roasting 101 - make one change at a time, take notes, taste it, make one change, take notes, taste it.... continue for a lifetime.

    Next suggested change, lower the heat when you get to 1st crack so you have a steadier ramp towards second crack.

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    Thanks heaps for the advice and tips Andy. Ill drop the heat from the max setting of 250C down to 200C after first crack next time and see if I can get a more steadier ramp to second crack like you suggest.

    Thanks again, Ill look out for that consulting invoice in the mail....
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  9. #9
    CoffeeSnobs Owner Andy's Avatar
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    The steady ramp makes it way easier to control that end of the roast and have some choice about where you finish roasting.

    Poppers suffer from a super-turbo finish to the roast and no easy way to dial the heat back, you should be able to control the toaster oven well.
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    So I had another go at this today. First go I had the heat on full (Oven temps were around 186C) and when I reached 1st crack I turned the dial back to 200C. I shut down about 1 minute after 2nd crack. But I ended up with a lot of divots in the beans where they have blown out.

    Second attempt I started at 200C (temps in the oven were around 130C) but after almost 20 mins the beans were nearly black and I hadn't heard 1st crack. I eventually heard 1st crack but pulled them out straight away as they were already black and starting to smoke a fair bit.

    Any suggestions?

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    Quote Originally Posted by Truman49 View Post
    So I had another go at this today. First go I had the heat on full (Oven temps were around 186C) and when I reached 1st crack I turned the dial back to 200C. I shut down about 1 minute after 2nd crack. But I ended up with a lot of divots in the beans where they have blown out.

    Second attempt I started at 200C (temps in the oven were around 130C) but after almost 20 mins the beans were nearly black and I hadn't heard 1st crack. I eventually heard 1st crack but pulled them out straight away as they were already black and starting to smoke a fair bit.

    Any suggestions?
    Bump..............Anyone???

  12. #12
    Senior Member fatboy_1999's Avatar
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    What were your timings for 1st and 2nd crack?
    If you are not already keeping records, start to do so.
    2nd crack + 1 minute is a pretty dark roast.
    Just my suggestion:
    Get a good ramp up to 1st crack. Say ~14 minutes
    Drop the heat for rolling 1st until rolling 1st completes.
    Try to get a nice gap between 1st and 2nd (2-5 minutes)
    Pull the beans just on or before 2nd.

    If you like them darker, you can go darker next time, but it's worth trying them at various stages.

    Your descriptions of temps above is confusing to me. You say the oven was @ 186C and then you pulled it back to 200C.
    I gather from the next part that the dial said one temp and the oven another, but for descriptive purposes, just stick to one.

    Hope that helps.

    Brett.

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    Quote Originally Posted by fatboy_1999 View Post
    What were your timings for 1st and 2nd crack?
    If you are not already keeping records, start to do so.
    2nd crack + 1 minute is a pretty dark roast.
    Just my suggestion:
    Get a good ramp up to 1st crack. Say ~14 minutes
    Drop the heat for rolling 1st until rolling 1st completes.
    Try to get a nice gap between 1st and 2nd (2-5 minutes)
    Pull the beans just on or before 2nd.

    If you like them darker, you can go darker next time, but it's worth trying them at various stages.

    Your descriptions of temps above is confusing to me. You say the oven was @ 186C and then you pulled it back to 200C.
    I gather from the next part that the dial said one temp and the oven another, but for descriptive purposes, just stick to one.

    Hope that helps.

    Brett.
    Thanks Brett,

    I cant find my notes on my timings but I think 1st to 2nd crack was around 4-5 mins. And yes I was saying the oven temp guage I used said 186C, but oven was set at 250C. Then I dialled it back to 200C and oven temp guage said 130C.

    So when you say rolling 1st do you mean the first time I here a crack? Ive noticed that I can hear a crack then a few more 1-2 mins later, then a few more again 2 mins after that. It seems like 1st crack goes on for 5 mins or so.

    So are you saying when I hear that 1st crack drop the heat a bit and leave it be for awhile?

    So should there always be a definite gap between 1st and 2nd crack? I always thought that you had to let 2nd crack finish too but next time Ill pull them as soon as 2nd crack starts.

    I was also worried that if my heat was too low and it took to long to reach 1st crack then you bake instead of roast the beans. How do you know when your baking instead of roasting??

  14. #14
    Senior Member fatboy_1999's Avatar
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    This is how I define the stages for my roasting:
    1st crack begins - when you hear a few cracks inside a 10 second bracket. 1st crack is often described as sounding like matchsticks snapping.
    Rolling 1st crack - a number of cracks, usually in pretty quick succession. Like when popcorn starts and then really takes off.
    2nd crack begins - when you hear a few cracks inside a 10 second bracket. 2nd crack is often described as sounding like cellophane rustling.
    Rolling 2nd - a number of cracks, usually in pretty quick succession.

    Your time between 1st and 2nd sounds OK. A bit longer than I usually go for, but you still get to 2nd.

    Going up through some of the earlier posts, it seems you are getting through the roast pretty quickly start to end.
    1st @ 8min and dump @13min is a little fast (but still will produce good coffee).
    Maybe see if you can add a bit more time on the length of the roast.

    My 'general' aim.
    From start to 1st crack - around 14 mins. When I want it to take longer, I don't go full heat right away. Ramp it up around 4 minute mark.
    14-16 min should take care of 1st crack. I use a 4 burner BBQ with hood so at this point I usually turn off all burners and let ambient heat take me the rest of the way.
    I roast outside, so the weather also plays a part. In Summer, I have to be careful not to go too hot as I can go straight from 1st crack into 2nd if the temps are too high.
    From end of 1st (~16 min), I keep an eye on the roast. I will see smoke from the roast prior to 2nd crack and I can usually pull a roast around 18-19 min mark without having hit 2nd.
    Sometimes I do hit 2nd (on purpose or not ), but I rarely want to go to rolling 2nd. That's just me.

    I think you are on the right track.
    As mentioned before, try to just change one thing at a time here.
    EG: Volume / temp / timing
    Keep notes and add tasting notes to the roasting notes once you drink it.

    So - to your questions:
    Rolling 1st would hopefully be a lot in reasonably quick succession, but different beans/heat profiles/roasting methods can all affect this.
    When you hear 1st start, you can drop the temp if you are trying to extend time between 1st/2nd, but you will need to play with your setup to find what is best for you.
    I always try for a gap between 1st/2nd. If they are too close or run from one to the other, then my heat is too high.
    How do you know when you are baking? Get to 20mins and no 1st crack (which I have done). It's trial and error to a degree. I often say that I think it is worth baking one and burning one to understand the limits. Although burning one can be dangerous, so have a fire extinguisher handy (should have regardless).

    Hope that helps.

    At this stage, it's probably information overload, but you are roasting for YOU right now. See how you go.

    Good luck.
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    I think my problem is I’m running from 1st to 2nd without realising it. I’ll gear a few cracks. Then I’ll hear some more which must be rolling 1st crack. Then a little bit after that maybe 30 seconds to 2 mins after I’ll hear some more cracks and I’m thinking it’s still more of first crack. Then the beans end up black and I realise I’ve gone too far.

    Im doing a roast now and I’ll record all my details. Thanks again.
    Last edited by Truman49; 2nd January 2019 at 12:59 AM.

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    Ok well here are the details of my attempts to night.

    1st batch
    1/2 cup Oven set at 200C on dial.

    5 mins - oven temp was 134C
    9 mins - oven temp 140C
    14 mins - still no first crack, turned oven dial to 225.
    16 mins - temp = 148C
    17 mins - temp = 152C
    17:30 mins - turned over up to full 250C
    18:20 mins - 1st crack, 1 bean
    18:42 mins - rolling crack temp = 167C
    19:30 mins - temp = 173C dial turned back to 225C
    20:30 mins - heard more cracks dial turned down to 200C. temp = 162C
    21:30 mins - more cracks not sure if still 1st or second crack but beans were black so pulled them out.

    Here is a photo
    IMG_2032.jpg


    2nd batch

    75 grams (just under 1/2 a cup). Oven set at 225C.

    2 min - temp=133C
    6 min - temp=160C
    10 min - temp=160C, 1st crack, 1 bean.
    11:30 min - rolling crack, dropped oven dial to 200C
    Pulled around 14 mins, didnt hear second crack

    IMG_2034.jpg

    3rd batch

    70 grams Oven set at 200C
    2 mins - temp=99C
    5 mins - temp=132C, set dial to 225C
    8 mins - temp=156C
    9 mins - temp=160C
    9:48 mins - 1 crack
    12:20 mins - 2 more cracks
    14:30 mins- few more cracks, could be considered rolling crack
    15:40 mins - drop oven setting dial to 200C
    17:30 mins - temp=143C
    19 mins - Pulled beans didn't hear a second crack at all.

    IMG_2036.jpg

    So from what I can tell out of this is that I need to have my oven inside temp at around 160C before I am going to get 1st crack. Also that the 3rd attempt was probably the best one but I should maybe crack it to 250C after 5 mins and then drop it back to 225C after 1st crack. What are your thoughts??
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  17. #17
    Senior Member fatboy_1999's Avatar
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    I think you are on the right path. Roasts 2 and 3 both look pretty good.
    Roast 3 is more like the profile I would aim for.

    The best feedback will be your taste buds.
    Let them rest for a few days (if you can) and do a side by side.
    If not possible due to the volume, then just jot down some tasting notes as you try each one.
    Make the notes relevant to YOU. EG: Don't try to describes notes of Juniper and Orange Blossom unless you have a palate that can actually make that sort of distinction.

    Enjoy the journey!
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  18. #18
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    Quote Originally Posted by fatboy_1999 View Post
    I think you are on the right path. Roasts 2 and 3 both look pretty good.
    Roast 3 is more like the profile I would aim for.

    The best feedback will be your taste buds.
    Let them rest for a few days (if you can) and do a side by side.
    If not possible due to the volume, then just jot down some tasting notes as you try each one.
    Make the notes relevant to YOU. EG: Don't try to describes notes of Juniper and Orange Blossom unless you have a palate that can actually make that sort of distinction.

    Enjoy the journey!
    I had a laugh..Thanks mate, will give it a go and see how it tastes. Ill save the wanky tasting notes for wine lovers as I certainly dont have a sophisticated palate like that.

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    I get very good results from a Hot Air Pop Corn pump. I have 2 types; The circular air motion and the vertical air. They both do a good job. I insert a metal (cloths dryer) pipe altered to fit both for the expansion. You can pick these up at Thrift Stores for approx. $5 -$6
    roger

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    I have been roasting with a KMart rotisserie for some time but with considerably more beans. My load has generally been 400gm and to start with I was getting first crack at about 12 to 14 min and finishing at about 18 to 20 min. With the thermostat set on full (250deg) I was getting an oven temperature of about 220deg pre heating for about 15 min. I was dropping the temp to about 180deg a minute or so into first crack and then pulling the roast when the colour was about right. Lately however I am unable to get the same temperatures with the oven and wonder if the thermostat is dying, and the times have increased to the stage I am getting first crack at more than 20 min, so think I am baking rather than roasting, and the coffee is disappointing.
    I am thinking of modifying the oven by removing the thermostat and getting a power controller to give more direct control over the elements rather than the switching of the thermostat. This should then operate more like the proper drum roasters.

  21. #21
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    I am thinking of modifying the oven by removing the thermostat and getting a power controller to give more direct control over the elements rather than the switching of the thermostat. This should then operate more like the proper drum roasters.
    G'day Ross...

    While an Electronic/PID Controller would afford you much better control over the temperature, have you checked that the heating elements haven't become encrusted with baked on coffee residues? Not uncommon unfortunately.

    Mal.

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    Senior Member deegee's Avatar
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    Quote Originally Posted by RossWB View Post
    I am thinking of modifying the oven by removing the thermostat and getting a power controller to give more direct control over the elements rather than the switching of the thermostat. This should then operate more like the proper drum roasters.
    G'day RossWB,

    I 've been roasting for a few years now with a Behmor, and longer than that with a couple of heavily modified poppers, which I still use for most of my roasts. I prefer the better control and faster response that I get from the poppers.

    To control the voltage to the 1200W heaters of the poppers, I use 3800W SCR 's . Some overkill there maybe, but that's the way I like it.
    They are very effective and reliable, and I have only had to replace one of them after six or seven years of regular use, (maybe because of the extra wattage rating). I bought them on FleaBay for less than $10 each.

    If you want to mod your oven, there are 5000W , and even 10,000W versions for under $20
    They should be sufficient to handle the 2Kw of your oven, even if the ratings are a bit "optimistic" which is sometimes the case with stuff on the bay.

    Cheers, deegee.
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    The bottom elements are pretty clean. They get a bit of chaff falling on to them which gets burnt off. I’m away at the moment but will be home early April, so I’ll give them a clean and see if that makes a difference.
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  24. #24
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    Behmor Coffee Roaster
    I was looking at a 4Kw unit from a home brewing supplier for about $50. Will take a look on eBay as well.
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