Deft. Coffee Roasters.

Been doing quite a bit of research and evaluation around the application of stainless steel as the contact surface.

The Pros
It doesn’t react with food. so the oils from the coffee can be wiped off the surface, leaving you with a drum that will not impart any flavor to the batch. It would be somewhat insulating to the roast environment… which would, in theory, make the roast environment more stable… It would be durable - not that the beans are that hard on the surface, but I think it may keep the drum from warping over time - a condition that seems to be a bit of a problem with older roasters—at least ones that are not well taken care of.

The Cons
I’m a bit worried that there needs to be an easy way to clean the surface of the drum, probably when it is still warm to remove all the oils from the surface of the drum. It makes sense to me that if they are not being absorbed into the metal (as they are when you have/season a steel drum) that they will turn rancid, and impart off flavors to the roast.—this may really just need to happen after each roast session though.
It’s a lot more expensive to use SS than mild steel.
It is a bit harder to work with, though not that bad, really.
It’s got such a low coefficient of thermal conductivity. It could easily have a tendency to get hot spots if not very very evenly heated.
—Not sure if this is a + or -, but it should be a good insulator of the heat inside the drum, making the process (slightly) more efficient.
Poor thermal characteristics would probably make the roasting environment less responsive to changes made at the flame.

Thoughts
Would likely be best if it were a very thin layer of SS - likely 1/64″. (looks like it’ll be about 1/16th thick).
In the end - what I am after is a drum that will have an high balance between responsiveness, even heat distribution thoughout the roast chamber, and with the added benefit of a non-reactive / durable surface… That leads to stainless, for the interior of the drum—as thin as I can manage—and a thicker outer layer of a good heat conductor to create even heat distribution. Wow, I just re-invented the All-Clad cookware. (!). Intuitively, I think that the pros outweigh the cons, with the caveat that the SS needs to be as thin as possible to minimize it’s thermal drawbacks.

I know that there are people who have toyed with this before, <link to rg post>. The thing is, that it is not readily available, and as far as I can tell, maybe only Smart Roasters (Kestrel, etc) have been the only ones to work out the specifics of this. I have heard of one SS sample roaster, but can’t find any information on it.

So, this leaves the outer material…
from what I can tell, I have two real choices: Copper or Aluminum. Copper being the obvious better choice - it is a better conductor of heat than aluminum, and undergoes less expansion than aluminum, by about 50%. Which makes it closer to steel (I don’t think that I will be able to get a clad piece long enough to make the drum—though I am considering piecing it together from several clad pots). However, I would rather go to something that could conceivably be manufactured, and that would pretty much exclude using a clad sauce pan… (but never say never).

But you can’t weld it—not that this is really a deterrent though, but I haven’t located copper tubing large enough yet—and I’m a little afraid of what the cost is going to be… We’ll see.