building a roasting drum - what material?

[zix]

Wey hey!
Since I am (not only reading but also) drinking too much coffee nowadays, it has become too much work using the heatgun to roast ´dem beans. I want to be able to make more than 200g per batch! Preferably between 500g-1000g, that would be an ideal level. Now: I have a BBQ grill (sort of), but finding perforated sheet steel to make a roast drum has proven... well, not impossible but difficult and expensive. However, perf sheet aluminum is easy for me to get, cheaper, and they are even willing to cut it to size for me.
This raises a question: can I use perf alu sheet for a roast drum? The melting point of aluminum is supposed to be around 400°C, so it shouldn´t melt but perhaps it might become soft and start "sagging"? Maybe ther will be other problems too? Anyone here with experience of using aluminum in a roast drum?

[matts]

Hey Mats

I can highly recommend the BBQ thing, just knocked off a 600g batch tonight which will keep me in espresso for just over a week I suppose, it's 20 mins start to finish once you have it nailed. Max capacity of my drum is about 1kg although I also do 200g small batches without problem.

Perforated stainless steel as you say is really expensive, and not the sort of stuff you want to try and work without the proper tools. I got my drum made up for me from bits that were already in the scrap bin at a stainless fabrication place, hence not too pricey, better telling of the story plus some pictures on my little website, there's a link somewhere on www.homeroaster.com and also lots of other barbie ideas there. No personal experience with aluminium but the measured air temp in the BBQ tonight was 350C at it's highest, is aluminium melting point not about 650C?, I'm sure it's been discussed on a.c. and people have built drums from it no problem.

Cheers
Matt

[zix]

Hey Mats

I can highly recommend the BBQ thing, just knocked off a 600g batch tonight which will keep me in espresso for just over a week I suppose, it's 20 mins start to finish once you have it nailed.

Ahh, that sounds more like it! That would be a perfect "batch size plateau" for me. HG roasting works fine, but not when you have to do it every other day.

the measured air temp in the BBQ tonight was 350C at it's highest, is aluminium melting point not about 650C?, I'm sure it's been discussed on a.c. and people have built drums from it no problem.

Well, to be honest I had not checked it up myself. 400°C is just what the guy in the sheet metal reseller place said to me. 650°C sounds a lot better! Think I'll go for the aluminium then, it is at least worth a try. A lot easier to work with too, as you said... Thanks!

[Danny]

Zix,... I've been HG roasting for a little while now.

I am finding it hard to get an even roast. I am using a ceramic bowl on a BBQ (low heat).
The HG is powerful and I move it round and round while I stir the beens in the opposite direction. Takes about 15 minutes.

I am curious as to how well you go.

[Ian]

Hey Zix, stainless steel would be the prime choice for drum material but in second place I would go for mild steel in place of aluminium.

Aside from the health implications (on which, the jury's still out) http://www.alzheimers.org.uk/Facts_abou ... minium.htm steel is much easier to work. Aluminium can be tricky to weld unless you are well practiced, one of my (professional) welders was notorious for producing what are known universally as pigeonshit welds in aluminium.

It would be unusual to get pure aluminium as it would be very soft, some sort of alloy would be more common. According to [Link removed at request of linked website] a food grade alloy is specifiable.

I have seen perforated mild steel in a DIY superstore but steer clear of galvanised (zinc plated) as the fumes given off would be hazardous.

Cheers

Ian

[matts]

Ian will mild steel not go rusty?

I never even considered doing my own welding, Ed at homeroaster.com seems to work wonders with riveting, I've never regretted my (relatively small) outlay at the stainless fabrication place.

Cheers
Matt

[zix]

Zix,... I've been HG roasting for a little while now.

I am finding it hard to get an even roast. I am using a ceramic bowl on a BBQ (low heat).
The HG is powerful and I move it round and round while I stir the beens in the opposite direction. Takes about 15 minutes.

I am curious as to how well you go.

Hey mrFollies! Thanks for asking. I´ve been busy finding parts for a drum roast and building it this week, so I haven´t been online a lot. Got the drum together today! Will be contributing with pictures and story for that one later on, it´s a bit... well, let´s just say it is a product of a slightly dented mind.
The HG roasting is going quite well, actually, and I get even results. I must underline that I often roast pre-blended, though, and that my roast *always* look uneven to begin with, but that they even out between first and second crack. I never roast more than around 200g, if I try to it becomes uneven and the roast takes too long (flat taste). I aim for at least 17 and no more than 21 minutes. Of course roast times are short(-ish) during the warmer time of year - not much difference though, unless I am roasting in direct sunshine on a calm day. I stick to the ceramic bowl, the dog bowl just doesn´t work for me.

Aside from the health implications (on which, the jury's still out) http://www.alzheimers.org.uk/Facts_abou ... minium.htm steel is much easier to work. Aluminium can be tricky to weld unless you are well practiced, one of my (professional) welders was notorious for producing what are known universally as pigeonshit welds in aluminium.

Thanks for the links, Ian. Yep, welding aluminium is very hard and I can´t even weld steel so alu welding is out of the question for me. I was going to thread the holes for M4 or M6 screws and screw everything together.
About aluminium and health risk: my initial thoughts about this was that since no water is involved in the process, roasting in alu might be OK. But you never know, so perhaps it is better to be safe than sorry. Too bad the s/s is both expensive and hard to shape. Galvanized likewise, apart from the fumes then - thank you very much for that tip, I didn´t know and would have been _very_ annoyed sitting there with a finished, smoking roast drum.

Still, what I use for now is not aluminium... heh heh, oh dear oh dear. I´ll get back to that.

[zix]

I aim for at least 17 and no more than 21 minutes.

mrFollies, perhaps I should add that as long as you use the same bowl, same heatgun and roast in the same environment, what matters most for HG roasting times is the amount of coffee that is in the bowl.
My 17-21 minutes roast time are with 180-200g of coffee roasted outside but shielded from immediate wind, with a 2000W Co/tech cheap heatgun in a deep, rounded ceramic (stoneware) bowl with approx 19cm outer diameter. The beans are stirred more or less throughout the roast, I stir less frequently if I want the beans to heat up faster and vice versa.
With, say, 100-150g total roast time will go down to between 12-16 minutes. Also, if it is windy, even just a little, roasting times will be too long without a windshield. This is the swedish west coast, with few calm days except for in June/July/August. I guess Amsterdam is also windy.

[Danny]

mrFollies, perhaps I should add that as long as you use the same bowl, same heatgun and roast in the same environment, what matters most for HG roasting times is the amount of coffee that is in the bowl.

Thaks for the info. I find that when I am getting closer to first crack I tend to slow down the stirring and move the gun closer to the brans. In some cases it means that the gun is actually stirring the beans itself.

There is a definate ramp up when I do this.

Anyway I wanted to know if there was anything majorly wrong with my technique, and the only thing I can see that you do differently is to be concerned about the wind. Normally I dont worry about this but I will start paying attention to it...

Thanks!

[Raf]

Interesting story, mats, I'm curious to see the result. Also: you can drink 600 g batches in under a week? By yourself? You must be some sort of walking caffeine hazard?

[zix]

Interesting story, mats, I'm curious to see the result. Also: you can drink 600 g batches in under a week? By yourself? You must be some sort of walking caffeine hazard?

Yeah, this is how I look and behave all day until my wife hits me in the head with a hammer to make me sleep:
quickIcantfindmyristretto whereismyristretto *eats the beans instead*
Nah - wifey drinks lattes almost every day too, and I usually manage to forcefeed a friend or two with a cup - or two.
Update on the roast drum story comes this week.

[zix]

Anyway I wanted to know if there was anything majorly wrong with my technique,

probably not, unless it could be the distance from the beans that is your problem.

and the only thing I can see that you do differently is to be concerned about the wind. Normally I dont worry about this but I will start paying attention to it...

I could take a photo of the bowl, of the whole setup if it would help you. I don´t have a video though, which would be infinitely more informative than a still image.
However, it does seem that you have your heat gun closer to the beans than I do. I try not to stir them with the air flow, not even close to first crack (well, to be honest the top beans will move around a little bit). I have full effect, max air flow (can´t do it any other way on my HG, it only has two settings) and try to keep the nozzle at least about 10 cm/4" from the beans. The distance probably helps in spreading the heat more evenly, and the bowl reflects the heat nicely (it is white and thick). Perhaps I have just been lucky? Or... perhaps I just happen to accept the slight variations in roast color where you don´t? I will take pictures next week of what I call an acceptable roast, that will be interesting.

[Danny]

Perhaps I have just been lucky? Or... perhaps I just happen to accept the slight variations in roast color where you don´t? I will take pictures next week of what I call an acceptable roast, that will be interesting.

Ok, sounds good. To be honest I dont have a problem with the result, but I was concerned about the fact that they coloured at different rates. I guess I had assumed that this may be a problem. You indicate that this is normal, so I guess I'll go on the same way but I'll take more notice of the wind.