Thermocouple place ment for DIY drum roaster - introducing the Rockabilly Roaster

[habahabanero]

After doing the popper thing over winter I decided I was going to have to upgrade after the first warm day took my roasts sub-5 min. The major criteria I set for my roaster were: ability to directly see and hear the progress (similar to the popper), mostly conductive heat transfer, optimal mixing, total control of the process, a 250gr minimum batch size and obviously cost. As none of the roasters within my budget really promised to deliver all the above, the Baby doesn't allow direct visualisation and the Diedrich IR1 is on the wish list for when I win the lottery, I decided I'd have a go at building one to spec. I've managed to cobble together a drum roaster that has exceeded all my expectations, but now the inevitable upgraditis has set in and I want to install a thermocouple!

I would prefer a bean mass probe, but I suspect it would get knocked around, as you can see from the first action pic there's a lot of bean movement - so will probably settle for an airtemp probe. The major issue is positioning of the probe and the heat tolerance of the lead - I suspect even the stainless braid may take a beating from being this close to the heat source. Any advice would be gratefully received, just keep it simple - there's a good reason this thing runs on a cordless drill!

I hope the images upload successfully - not much use if I rabbit on about the thing and no-one can see what I'm on about.

Dave

[Mono]

Hi Dave, nice adaption to the drum system. Looks like a "brikkie's" mixer. My thoughts are to run it up through the shaft but then it would need to be hollow and wouldn't work with the cordless drill system. I see your problem with the heat source, maybe you could shield a probe coming into the front opening of the drum? Personally I would leave things alone and use sight, sound & smell.

Steve

[flynnaus]

I would say your design doesn't lend itself to the traditional thermocouple - bead or probe, because of the rotational movement and agitator design. You could try one of those temperature gun type thingies where you point it at the heat source. They can be quite expensive but you can get at least one model from fleabay for less than $100. Dunno whether one can be hooked up to a data logger though.

[fg1972]

Nice design,
Temperature monitoring would be nice, but at least you have direct sight of the beans.
I had built an enclosed drum roaster (no direct sight of the beans) and tried running a thermocouple in the centre of the drum via a hollow shaft which did not work too well as the cable sometimes caught & started to spin.
In the end I sold the roaster as I didn't feel comfortable roasting without sight of bean colour & no temp monitoring.
I'm most likely going to get a Behmor once I can secretly come up with the funds as my other half would loose it if I spent more money on coffee equipment.
Until then, it is roasting with a thermocouple fitted popcorn popper for now.

[habahabanero]

Thanks for the advice guys - pretty much confirms my thoughts that a thermocouple isn't going to be an easy addition to the "brikkie's mixer". I was wondering if anyone has any idea how heat resistant the stainless braid is?
I've also just realised the biggest barrier to pimping my roaster with a thermocouple is the additional cost of parallel for mac - so I can run the free software - life is cruel.
I had a good look at your design when you first posted it fg1972 - very impressed, but when I built a prototype (perversely, out of an old Illy tin) I came to the same conclusions as you, firstly that I had to be able to see what was happening, and the fact that my other half would rip my ear off if I spent more on coffee gadgets

[sando]

Hi Dave
What a great idea you have there.
When I first started roasting I only had access to an infrared thermo. Its a Raytech ir thermometer. Just point at the beans and you will get the temp instantly, and acurate. I used it with good results for about 12 months. Its still part of my setup and I keep it handy for checking temps around the edges of my roastery. I think I have seen them for about $20ish on the bay of evil.
Could put it on yr Xmas list??? Not to late??
Try searching IR thermo.
Cheers
Sando

[habahabanero]

Thanks Sando

I think I'll probably have to go with the IR thermo idea, on rechecking my set-up there is clearly no way any bit of electronics is going to survive the heat coming past the drum. The major reason for wanting a thermocouple is repeatability as I have as much control as needed. I have considered using a heat gun aimed at the side of the drum as heat source, which will at least allow me to standardise things a bit more, and I could then take a thermocouple lead near the drum. At this stage I'm enjoying the simplicity and "seat of your pants" approach of the gas stove set-up

Dave

[DesigningByCoffee]

We have family friends who grow/roast their own beans down the south coast, and he roasts in a larger commercial gas powered / electric motor roaster similar in concept to yours, but with 3-4kg batches. He uses an IR gun for his temp checking.
Just as an aside - I tasted the cherries straight off their trees, then also had a coffee through their home machine and mine at home - and it all had a quite strong peppermint edge! Beautiful! Never had any coffee like it before on since - a SO coffee that tasted like after-dinner mints :-)

Matt

[habahabanero]

I'd be interested to see pics of his set-up, Matt - always looking for opportunities to improve mine. Just a question - when you said South Coast, did you mean he's growing coffee south of Sydney?! My tree has been so slow here on the Central Coast I'd think any further south would be impossible.

Dave

[DesigningByCoffee]

Hi Dave
Unfortunately I haven't got a pic of his roaster, but got some of his farm and pulper. He is actually doing it more as a hobby (50 trees?) down at Gerringong on the south coast. I think you'd struggle to go too much further south, though there used to be a plantation down at Berry…
His roaster looked like a narrow cement mixer with a gas ring down the back I think… didn't see it in action though.
I'll try track down some pics…

Matt

[DesigningByCoffee]

Hi Dave
As promised, a couple of pics…
I did have a 3/4 rear pic of the roaster - as you can see it is substantial, and has a shroud. From memory, it was chain driven, with a rotating perforated drum inside, and the front open for chaff venting…
The interesting thing here is that all the trees are grown under the canopy, and well protected from the frost/wind…
Cheers Matt

[habahabanero]

Thanks for the pics, Matt. The roaster is an interesting format. I'd love to have 50 trees as a hobby, sounds like great fun!

[DesigningByCoffee]

Doesn't it ever! :-)