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Thread: BBQ Heat Diffusion, rocks/ceramic/iron?

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    BBQ Heat Diffusion, rocks/ceramic/iron?

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hi All,

    Im new to the forum, so howdy, brief speil about me is that Im a novice roaster, after getting down the basics, a chance trip to the local farmers markets has led me to look at opening a stall. Marvelous I thought, Ill build a drum roaster, set it up, order in coffee, tweak and tune and in a few months Ill open a stall to wile away the early hours of Sunday morning.

    Then I was informed that the Markets want me up and running in a fortnight *:-? And yes, this is just a hobby for me, I do have a 9 to 5 regular job...

    Basically the markets are moving to a new location, and are having a grand reopening. Will give the markets a nice air to have a bloke out the front roasting some beans, and will give me a chance to let people know Im out there. Win Win. With the tinkerer within me suitably stirred, I retreated to the birthplace of all great Australian gear. The shed. Two days later I re-emerged, weary and bloody but clutching my new drum roaster tightly to my chest. Then to the internet, and frantic ordering of bags and beans, which hopefully are in transit.

    BTW I have to say a big thanks for beanbay! How brilliant! The prices for the Peruvian Ceja de Selva beans are a third of the cost elsewhere! Andy Freeman, we havent had a chance to correspond yet, but thanks again, and thanks to the whole coffee snobs community for supporting this excellent resource!

    After an extended scrounging session a bbq was found to house the drum, and now after that not really brief at all opening spiel I come to my question.

    Currently Im getting a distinct heat zone in the centre of my setup, I can actually see the beans in the centre hitting French while the edges are barely at city. I need some sort of diffuser to get an even heat profile, Im thinking at the moment of making a basket of volcanic rock to lower over the long lengthwise burner, but am unsure if perhaps iron or ceramic is a better option... any thoughts?

    With that sorted I have only to replace the glass view panel in the hood, sort out a better means of removing chaff, and then figure out how the whole kit and caboodle is going to be fitted to the motorbike... A sidecar might be in the wings... why a motorbike? Well wouldnt be a cafe racer roast otherwise, and when was doing things the easy way ever any fun?

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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    Quote Originally Posted by 6461726D7374726F6E67000 link=1245821278/0#0 date=1245821278
    Two days later I re-emerged, weary and bloody but clutching my new drum roaster tightly to my chest.
    this thread is useless without pictures !!!

    go get your camera !!!!!

    good luck with the new venture :)

    ps welcome to coffeesnobs :D

  3. #3
    Senior Member fatboy_1999's Avatar
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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    Welcome to the site CRR,

    I personally use volcanic rocks on my BBQ roaster.
    I have a 2 part grill that lives there for the cooking of meat, but I just use the exposed rocks when doing coffee.


    However, your heat zone could also be caused by lack of rotation speed and/or agitation of beans.

    What volume are you roasting each time?
    What is turning the drum and how many RPMs?
    What did you use inside the drum to agitate the beans?

    Brett.

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    Senior Member Koffee_Kosmo's Avatar
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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    I was just about to say that fatboy has volcanic rocks on his BBQ roaster ^^

    You have 2 weeks to play and tweak if one way does not work try the next

    I reckon 50 - 55 rpm is what you need for your drum speed

    PS
    Welcome to CS *;D

    Roasting is fun

    KK

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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    I promise nothing pretty, but will have a picture in the next few days, once I get the last little peices in place. Dont want to publish pictures to a dodgy setup! Might lead folks astray!

    Ive been pondering the rotation speed, have been using a rotisery, which is giving a rather sedate 6rpm. Ive got fins (technical word?) running the length of the drum for agitation, and have had no problems with stratiation of the beans vertically. Instead having the distinct hot spot in the middle with the ends running cool is giving me the horizontal stratiation. Now Ive got a basic setup Im going for the tuning method thats served me well with my bikes, one change at a time and test it.

    Im thinking with the distinct hotspots the first thing Im going to want to target is the diffusion to spread the heat out, I think its radiant heat from the flames causing the hot-spot. Once thats out the way then up the rotation speed.

    While in the design stage I made the choice to have a large window running the length of the drum, partly for people wandering by to have something to look at, and partly so I could monitor the entire roast continuously to pick out where I was dealing with heat buildup etc... In hindsight I guess the setup actually makes a pretty neat test bed... Ill start taking some pictures for prosperity.

    Oh and Ive bean building (pardon the pun) to a 250g roast so far. My stocks are really limited atm, switching from roasting just enough for myself and setting up a new roaster has really eaten up my tiny stockpile! Eventually Id hope for kilo... may need a larger drum to achieve that... but time and roasts will tell!

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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    Quote Originally Posted by 3B3C293F3224026C6464645D0 link=1245821278/2#2 date=1245821821
    I personally use volcanic rocks on my BBQ roaster.
    I have a 2 part grill that lives there for the cooking of meat, but I just .
    not wanting to run off topic but fatboy are there any chaff issues inside that drum?
    do they burn in the drum?
    or fall out and ???
    what speed do you run at?

    might help CRR in his building as well

  7. #7
    Senior Member fatboy_1999's Avatar
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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    Quote Originally Posted by 232F262B2B224E0 link=1245821278/5#5 date=1245824452
    Quote Originally Posted by 3B3C293F3224026C6464645D0 link=1245821278/2#2 date=1245821821
    I personally use volcanic rocks on my BBQ roaster.
    I have a 2 part grill that lives there for the cooking of meat, but I just .
    not wanting to run off topic but fatboy are there any chaff issues inside that drum?
    do they burn in the drum?
    or fall out and ???
    what speed do you run at?

    might help CRR in his building as well
    Chaff does gather in the drum. Of course, it depends on the bean too. A dry processed Brazil produces a lot more chaff than say a washed Sumatran. Some chaff burns off during roasting, but the rest gets blown away during the cooling process. I have a fan on its back blowing upwards through the area the beans are dumped.

    My drum is run by a car windscreen wiper motor and goes at around 55rpm.

    My drum does a kilo (green) with comfort. In fact, the roast in the picture is 1010g of Peru Grace Estate. It yielded 868g roasted.

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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    OK, Rocks in place, and have also finished repairs to the hood so that it seals in heat properly now with a venting port running the length of the back. Have sourced a windscreen washer motor, many thanks to fatboy for the headsup on that one. However I have one little issue.

    Heat buildup has gone up considerably. A test roast after sealing the hood resulted in ashed beans in 5 minutes. More alarmingly what Id believed to have been an extremely vigorous first crack had me diving for cover when shrapnel started pinging off the top of the hood and bangs like a rifle shot came from the roaster. The volcanic rocks Id been using for diffusion had exploded. Ive been careful to keep them dry, so no idea how the moisture got into them, but after killing the gas, donning my tin hat and hiding behind the outdoor setting, I later returned to the then cool BBQ to find the rocks now had an appearance of honey comb.

    Im partly to blame for this, Id been tinkering with the burners to get a clean burn. I certainly achieved that by adding a oxygen port, instead of a soot causing yellow flame Ive got a burner producing a clean and hot blue flame. Heat regulation will be via fuel supply as normal. However this flame appears to be hotter than hell, Ive just ordered a temperature logger to figure out what temps Im actually hitting, but Im mighty worried about these volcanic rocks.

    Is it normal for the rocks to "pop" and form a honeycomb structure? Im thinking maybe some moisture got into the bag of rocks I bought at bunnings or something.

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    Senior Member fatboy_1999's Avatar
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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    I havent put new rocks on a BBQ for some time, but I do recall them making some crackling sounds for the first few times they were used. I dont recall firey shrapnel though. Might be worth reading the bag to see if there are any warnings/advisories for first use.

    The rocks on my BBQ do have a porous look and quality which is what I gather you mean by the honeycomb look.

    The hood on my BBQ in no way is a perfect seal. Plenty of heat escapes, Im sure, but I have a thermometer in the hood that I keep an eye on. Trial and error has taught me that the indicative temperature I need to be aiming for is around 260 according to the thermometer. If I go over this by too much, I need to vent some heat but usually burner control takes care of things.

    Do you have any temperature monitoring method, either ballpark (like mine) or more accurate (thermocouple) that you can employ to avoid future 3rd crack roasts?

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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    Not yet, a logging thermocouple from beanbay has been ordered after plodding around to every bbq and hardware store in the area turned up nothing. Was originally looking to have two manual thermometers over each of the burners to give me an indication if one was running hot, but everywhere only has meat thermometers that stop at around 220 degrees. One place agreed to order one in for me if I could provide the make and model of the BBQ I wanted it from, but as this is a custom job I made the call to just buy the beanbay thermocouple and make my life a lot easier but having the software do the profiling work for me.

    Though if anyone has any leads on cheap thermometers with a suitable range Im all ears. I come from a line of engineers, and its hard coded into my genetics that I get a perverse pleasure from tapping guages on machines and scratching my chin.

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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    More alarmingly what Id believed to have been an extremely vigorous first crack had me diving for cover when shrapnel started pinging off the top of the hood and bangs like a rifle shot came from the roaster. The volcanic rocks Id been using for diffusion had exploded. Ive been careful to keep them dry, so no idea how the moisture got into them, but after killing the gas, donning my tin hat and hiding behind the outdoor setting, I later returned to the then cool BBQ to find the rocks now had an appearance of honey comb. [/QUOTE]

    Hi,
    Um, just a thought, did you season your volcanic rocks????? As in, once you put them on the grate did you turn your burners on to high, drop the hood & step back to eliminate the exploders (air pockets? from memory)?
    Which markets are you starting up at?
    Good luck!

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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    Hi CSrs,

    I think I saw oven thermometers at Aldi within the last week or two.
    Under $5 maybe.
    Worth a drop in if passing by one, Perth does have Aldis?

    Lindsay


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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    Quote Originally Posted by 494C4B4156445C5744250 link=1245821278/11#11 date=1246796950
    Worth a drop in if passing by one, Perth does have Aldis?
    We dont have Aldis as yet here in Perth, maybe in 10 years ;D ;D ;D ;D

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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    An oven thermometer! Of course, Ive been running around looking for BBQ thermometers, will start looking in the kitchen/cooking stores. Geez talk about me being stuck thinking inside the square.

    I think I may have inadvertantly seasoned the heck out of them. Ive had another crack and theyd settled down a bit but I think few more full throttle runs is gonna be needed before I wheel the contraption out in public, just to be sure. Im mighty glad youve mentioned they need seasoning though, was nothing about it on the packet and Id been mighty concerned around the rocks ever since.

    Ill be setting up at the Armadale Producers markets, located in Kelmscott at the hall next to the oval. Hopefully will be up and running next weekend, missed the grand opening unfortunately, theres a fair bit of background work needed! Currently trying to sort out how I can offer a sample of the beans, was hoping to get approval to bring in a few thermos and disposable shot glasses, but while I was worried about meeting health n safety guidelines ended up running afoul of a non-competition policy. Market has a bloke with a coffee machine on the side of his pie and sweets stall. Last chat with the organisers they suggested I give people the beans then send them over to the bloke to have him make the coffee for them. Well its fair enough to say, negotiations continue *;) Trying to make sure I dont do the wrong thing by anyone, but Im sure folks around here can testify that beans alone dont determine the taste. I wont pretend to be a master of the roast, still just a beginner, can make coffee that I like, but now Id like to figure out what type of coffee everyone else likes, and to do that I need to give out accurate samples of what Im providing and be able to listen to feedback.

    BTW snobs are more than welcome to swing by and give their thoughts, bit of a nerve racking statement to make as Im strongly suspecting they wont be to impressed during the early days, but I reckon Ill learn a lot from the criticism of a snob so I say bring it ;)

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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    Quote Originally Posted by 3431223D2324223F3E37500 link=1245821278/13#13 date=1246846747
    An oven thermometer! Of course, Ive been running around looking for BBQ thermometers, will start looking in the kitchen/cooking stores.
    I think from memory House has them for around $15, they arent very precise though??

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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    Quote Originally Posted by 7D7664717A76607D7C71130 link=1245821278/14#14 date=1246856270
    I think from memory House has them for around $15, they arent very precise though??
    As a starting point, they dont need to be precise, just consistent.
    EG: If it reports 220 degrees as 230, then so be it. As long as it ALWAYS reports 220 as 230, then at least you have a reference point.

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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    Newbee ur a legend, now I just need to figure out where the nearest "House" is. Ive seen the shop before, a sort of homeart kinda store, but I dont think my local centre has one. Time for a yellowpages and a few phonecalls.

    Fatboy ur bang on the money. Ive got a thermocouple possibly waiting for me on my doorstep as we speak, which Im planning on fitting to the middle of the roaster and hooking up to a netbook to datalog the profile, but Im spinning a 50 to 60cm long drum with a long split burner underneath (can control each end of the burner seperately) Having a rough idea of the temperature zones over each burner will allow me to make sure that Im getting an even heat, plus giving me more dials and guages that I can pretend to understand *glee*

    I should probably add some on-topic info in case in the years to come someone else is in my shoes. After "seasoning" (a.k.a. uncontrolled explosions) of the volcanic rocks I roasted a new test batch. Temperature gradation from one side of the bbq to the other was much improved. From there a windscreen wiper motor was purchased ($30 from a local magna wrecker, just ring local wreckers and ask for a windscreen wiper motor. Theyll ask for a model of car, just tell them you want a motor to spin something at about 60rpm, you want the cheapest one. Some will spit the dummy and demand you supply a car model, dont bother doing business with them. Vast majority will be cluey enough to be able to sort you with a suitable motor.) After purchasing the motor was wired up. Mine had four wires, find the ground wire, then one of the wires will be for high speed, the other low. I believe the fourth wire will control direction... no idea about that to be honest. I hooked up a three way switch so the motor can be run fast or slow, for coffee I run it fast at about 50 rpm. Slow might come in useful for a delicate roast... tea or cocoa or something... I dunno. The motor runs on a 12V DC power supply, so makes for a handily portable setup.

    Cooling and chaff removal remains an issue. My initial brilliant idea was based on a oversized popcorn maker. Looking at how the beans would be spun around the base of the maker I decided it would make an elegant cooling solution, circulating and cooling the beans in one go. A large milo tin was secured for the chamber, louvered vents punched in around periphery of the base of the can, then the whole lot dropped into a larger can and sealed up to make a manifold. A 12V "squirrel cage" blower hooked up to the larger can and let rip. No-where near enough power to spin the beans. So a leaf blower sitting nearby on the verandha is fired up to see if the concept itself will work. Spun the beans nicely until in my excitment I leaned forward to see if the beans were spinning properly. Long story short I accidentally made a seal with leaf blower to the manifold, and half a kilo of freshly roasted peruvian beans rocketed out the top like a shotgun blast and soared over the fence to land in the neighbours pool.

    Theres been some...tension... since the Australia day beer rocket assisted roast chicken accidentally landed in the same pool but luckily the neighbour was out so a quick fish around with a net got rid of the worst of it. Think Ill swing by a "Home" on the way home tonight and grab some thermometers, will try and get a picture of the setup as well.

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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    Quote Originally Posted by 2B2E3D223C3B3D2021284F0 link=1245821278/16#16 date=1246863359
    Newbee ur a legend, now I just need to figure out where the nearest "House" is. Ive seen the shop before, a sort of homeart kinda store, but I dont think my local centre has one. Time for a yellowpages and a few phonecalls.
    Aw shucks, 8-) thank you :-[ :-[

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    Re: BBQ Heat Diffusion, rocks/ceramic/iron?

    Behmor Coffee Roaster
    Surely theres a House in Kelmscott or Armadale?



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