Flower Power Cement Mixer Roaster

[forrest]

My "roaster" might give some of you a bit of a laugh. I had read up on using the old popcorn machine for roasting and was about to head out to pick one up, when my engineering brain slapped me and set me the challenge of building something workable using what I had lying around. (Could have also been the wife's voice in my head asking why I needed to buy more coffee related equipment after buying the new Lelit, eazytamp, etc etc...)So I gathered up some bits and pieces and put together a small 'cement mixer' style barrel driven by a cordless drill, with heat provided by an XU1 hot air gun. The barrel was an old Ikea tin; I find the design on the sides of the tin really helps bring out the floral notes in my roasts.





I installed some simple mixing paddles/strips up the sides of the barrel to help agitate things. Basically I hold the drill in a bench clamp angled at about 20 degrees backwards, use another clamp to get the drill rotating slowly, then hand hold the hot air gun at the opening (moving closer or further to regulate temperature). I set the hot air gun to it's lowest heat setting which from the spec sheet is apparently 300 degrees celsius, and I assume about 1000 watts. I have played around with holding the gun closer and further away and by doing so have reached first crack as early as 8 minutes and late as 13 minutes. I also have an IR thermometer which I have played around with during the roast however as yet have not had a huge amount of success with repeatable/useful readings, which I imagine is a lot due to variations in emissivity of the beans as they go through the roast cycle. I have been roasting 200 gram batches with relative success (not that I have anything to compare to!). Have done 8 roasts so far, the photo attached is from the very first roast. The results seem to be fairly even in roast colour, although there is some variation due to bean size.




Was quite a fun little project, and the end result is far better than I could have expected! Further modifications to come of course...

[Philby1981]

Great work!! I can see a mod idea of fixing the heat gun in position and putting the drill/drum on a sort of slide roller to move in and out (closer or further to heat gun). That way you can put markers on the bench or slide unit at intervals if roast when you find sweet spots in temps etc to make profiles that bit more repeatable.
Again good job, I love coffee innovation

[forrest]

Yep exactly what I was thinking! Would be great to get some easy repeatability (and reduce the chaff shower which I currently get holding the gun in front of the drum haha)

[forrest]

Actually the thing I would like to get sorted is a reliable method of temperature measurement. The drum style makes using a thermocouple extremely difficult... any ideas?

[Philby1981]

Great idea If anyone is really technical. Thermocouple that is wireless using wifi network on your laptop, iPhone or smartphone. Would make data logging easy. Maybe even have one sturdy enough to have it like a little ball that just goes in with beans. Surly this must be doable if not already done. Would just have to remember to take it out before it goes in the grinder

In the meantime you may be able to rig up a bead type one into bean mass. Run it through the front possibly anchored to heat gun exterior or other non turning part. Just got to be careful it misses the paddles

[Kevo]

Was quite a fun little project, and the end result is far better than I could have expected! Further modifications to come of course...

Like Philby says; "love coffee innovation". Well done!
Not too sure about the use of what looks like galvanised materials though.
I won't entertain high temp cooking of food with teflon, let alone galvo!

[forrest]

Yeah good point Kevo, I actually looked into that a fair bit and deduced that the risk of any significant (harmful) amount of zinc transferring to the beans at these temps was negligible (and certainly if anything much less than the zinc tablet I take every day!). I also soaked, scrubbed the pot and heated up very hot with a torch first to see if anything burned or fumes were produced and there was nothing so I am confident there isn't any risk with it. Should always be careful though! If I'm not mistaken a lot of the popcorn makers look to have galvanised/zinc plated steel chambers in them as well?

[forrest]

Philby, not joking I had this exact thought the other day! Would be a brilliant way of knowing what is going on inside any roaster and make data logging so easy.

How hard could it be?! haha

[Javaphile]

If I'm not mistaken a lot of the popcorn makers look to have galvanised/zinc plated steel chambers in them as well?

I would doubt that very highly as galvanized zinc is not classed as a food safe material and the last I knew in the US its use is banned in any situation where it may come into contact with food.


Java "Tin yes, galvanized zinc no." phile

[forrest]

Fair enough my mistake, just looked at a few photos of chambers and they looked to be but agree are most likely tin. Re: food contact, not quite what I had read during my research, for example: In Contact with Food | American Galvanizers Association. I know a lot of water tanks are zinc galvanised as well, including one where I grew up, and other than the 11th finger I have sprouted I am fairly healthy... I am not advocating it's use for anything and think people should always do their due diligence where health issues are involved, just saying that after my research into it I was not concerned for this application (dry conditions + relatively low heat compared to zinc fume/melting point - roughly 420c).

Besides, this is all good support to convince the missus I need to invest in some shiny stainless

[MrJack]

The roast chamber itself is aluminium (in my 4 poppers), but the chamber beneath could well be electroplated zinc. Tend to have a yellowish tinge (passivated?).

[Javaphile]

Interesting. I hadn't looked at it from any direction other than the code for kitchen/restaurant type settings where any use in a direct food contact area is strictly forbidden here. Reading through the more general FDA regs I can see why it would be banned in a those settings due to exposure to the acidic foods found in virtually every kitchen/restaurant.

Besides, this is all good support to convince the missus I need to invest in some shiny stainless

Well there ya go! Forget those pesky liberal FDA regs! Go for the Bright & Shinny!


Java "Another grey cell filled" phile

[forrest]

haha exactly... I am currently working offshore and there is a fair bit of aluminium and stainless scrap lying around, I might need to organise some excess baggage allowance for the chopper home!

I am actually very excited about designing and building a more substantial roaster with temperature monitoring and control etc. Some great information on here from various DIYers. I quite like the challenge of incorporating off the shelf items into a design as well.