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Roasting with a K-Mart convection oven

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  • RossWB
    replied
    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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  • RossWB
    replied
    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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  • deegee
    replied
    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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  • Dimal
    replied
    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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  • RossWB
    replied
    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.

    Leave a comment:


  • oldboybrewer
    replied
    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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  • Truman49
    replied
    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!
    LOL..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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  • fatboy_1999
    replied
    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!

    Leave a comment:


  • Truman49
    replied
    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
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    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

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    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.

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    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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  • Truman49
    replied
    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; 2 January 2019, 01:59 AM.

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  • fatboy_1999
    replied
    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.

    Leave a comment:


  • Truman49
    replied
    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??

    Leave a comment:


  • fatboy_1999
    replied
    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.

    Leave a comment:


  • Truman49
    replied
    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???

    Leave a comment:


  • Truman49
    replied
    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?

    Leave a comment:

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