I have been slowly building a gas powered roaster over the last few months. This project has been largely spurned on by lustful roasters like Jon R's 1lb US Roaster

US Roaster Co. 1-lb Sample Roaster

and Ken Fox's Diedrich 1kg IR1

My days of being dogmatic about roasting are over

and a small salvo of of posts about the value or a rotameter http://www.omega.com/prodinfo/rotameters.html for gas control. You will notice a good bit of similarity between the early stages of mine and and DJR's 32 oz milk jug roaster

Making Your Own 32 Ounce Roaster.

This is both incidental and inspirational! Here a a few early shots:






It is a "Probat style" roaster with combustion below and cross flow of gas from rear to a port out the front. I will have a cooling tray in front and gas pulled by a blower mounted in the rear. Not shown is the motor mount I welded up today and the motor that will spin the drum at 60rpm. If anyone has hints or advice or what features I should integrate I would love the input. The Idea is to be fully manual control by needle valve and metering with rotameter. I will install at least 2 thermocouples for BT and ET and monitor via Artisan software. I also want adjustable airflow. I'm thinking a DC centerfugal blower with a pot to control speed. I haven't computed what flow I will need so advice is wanted. I am "crowd sourcing" this roaster here so please chime in!

Looks like nice work! My roaster runs at 90RPM, but 60 ought to work. You'll need vanes. I didn't notice a difference between 2 and three when I did mine. One would probably suffice. Not clear how you'll empty it.

I suggest you skip the blower, instrumentation and for gas just get an outdoor cooker ring (about $40). Try it and see if you like the results.

One thing I'd like to understand is the whole idea regarding forced air flow. If someone could explain what purpose it serves, I'd appreciate it. To get controllable roasting times with a setup like yours is very simple and measuring the inside temperature of the beans is also simple using an IR hand held thermometer.

I've been thinking of making an aluminum shroud over mine, but it isn't high on my list. I roast 4-5 pounds a week and climbing and it is so simple and reliable I'm finding it hard to improve.

dan

Are you keeping an eye on temp ratings of bearings and other materials that will be exposed to the high heat of the roasting environment?

Len

I wondered about this and solved the problem by using a fairly large shaft that doesn't get very hot and by using wood bearings, which were supposed to be temporary, but are actually ideal and after more than 300 roasts, show no signs of deteriorating. I do spray them with water at the beginning of the roast, but I have also forgotten to with no adverse affects. I can pick up the drum by the shaft at the end of a roast and it is warm, but won't burn me.

I was going to use a bronze bushing bearing and a high flash point oil, but there really is no need. I personally would have made the shaft in the roaster, above, larger in diameter, but it might not matter.

I used a bronze bushing good to about 500f and it should require no lubrication. The shaft is carbon steel and is 5/16s. I chose that size because it it was the same diameter as the motor shaft and the coupling was a lot cheaper for like sizes. I will definitely add vanes, I'm just pondering the sleekest way to do it. I want to do the forced air setup because I will be roasting inside and want to vent directly out the window. I also just assumed that it was better that way because the pros do it that way. Maybe I should rethink that but I'm assuming the idea is to control the balance between conductive and convective heat transfer. I have a crazy thought to do the whole front or at least part of it in heat resistant glass. I will probably do the peak in steel and have the hinged discharge door made of glass, as long as the price isn't crazy.

My vanes are made of perforated stainless steel and protrude about an inch. They are angled so that they move the beans towards the front of the roaster. The entire roaster is angled so that the beans tend to slide the other way, causing a mixing front to back.

I think you could get away with just one vane.

You really should consider using the roaster as is, to try it and work out any bugs rather than building everything and then debugging, at least, that's my opinion.

I'm still trying to figure out what I might gain by using forced air. I'm not against it, I just want to understand the advantages???

I'm still trying to figure out what I might gain by using forced air. I'm not against it, I just want to understand the advantages???

Some of the advantages are:
Chaff extraction. Pretty obviously, to remove the undesirable silver skin itself but also it will reduce the taste of roasted chaff from the beans.
Smoke extraction and control. Extraction of the smoke is essential, for me, to reduce the smoky taste that could result from extended exposure of the beans with the roast smoke. This is most obvious on dark roast.
Of course some smoky taste may be desirable, to some, but having a means to control the amount of exposure would be good. Also, if one wants to exhaust smoke outside, forced air makes it easier and more efficient.
Improved Temperature control. Forced air allows much more control on the roast environmental temperature over heat power alone.
Improved Convection roasting. This is the most desirable, for me, benefit of forced air. Convection roasting provides a much more controlled and even roast than conductive roasting. Of course, even without forced air there is some convection, especially if there is a lot of mixing happening.

Although these advantages can (and surely will) be debated, these are all in my (limited) experience very desirable. YMMV

Thanks, that was helpful. In my case, since I roast outside, I guess I'll not do forced air.

The chaff issue is also a non-issue, again because of outdoor roasting. A lot of it exits from the perforated holes in my drum and the rest is completely eliminated by the dust collector which is powerful enough to remove almost 100% of the chaff through the colander.

Control over heat is also a non-issue (only for me, not in general) because the burner and low thermal mass of the drum quickly (in seconds) allows me to increase or decrease the heat.

If I was roasting indoors, or even in a garage, all of the above would have to be revisited. I'd probably use the dust collector on a VFD to control airflow and to cool beans and to exhaust the smoke.

My setup is pretty funky and silly looking, but for some reason even though it is simple, it generates very even and controllable roasts of 32+ ounces in 12-20 minutes depending on how I want to ramp things.

I think if I wanted to increase the capacity, I could maybe triple the size, put shrouding on to conserve heat and as a safety measure. I wouldn't trust the wood bearings in this case, unless I moved them further from the shaft and increased the shaft to 3/4" or so. I don't think I could scale the design much bigger than that which would be 5+ pounds. If I did it I'd probably go to a box shaped drum and dispense with the vanes, at least at first and see how it worked. It should work, I think.

I just had an "ITS ALIVE!!!!" moment. I made the motor mount and cut the shaft to the right size and mounted it all up. The AC gear motor works great and 60rpm should be perfect. I'll post pictures when I get a chance. Anyone with tips on what exhaust fan to use and control method would be great. I also don't know what a typical air flow in CFM is. I am also concerned about the temperature of the gas and what the fan can handle. Thanks!

You got to just try it now!