I would like to hear your opinion about the best material to use for a drum roaster.

I quote from a roaster manufacture document:
"..... we use carbon steel because it contains the best of these metallurgical properties, is durable longterm
and cost effective. Many people think stainless steel or cast iron is better however this is not the
case in regards to "evenness" of retaining and disbursing heat across the entire drum and transferring
that evenly inside the drum to the bean. This is also a fallacy as stainless steel is not as effective because
it is a reflective metal that dissipates the heat differently and cast-iron is a porous metal that has uneven
density.
Since cast iron is "poured' in to a mold, the density is not consistent throughout and therefore the
thermal dynamics of heat transfer is not even. Carbon steel is rolled and the density is consistent in its
thickness - the result is "evenness" in the thermal dynamics of heat transfer. Please note however, the
steel used and the engineered design of the drum is only one element of consistency in a ... roaster."

Thanks for your opinion.

Good engineering thought problem here...which material is best?

What is best from a "Temperature Standpoint"

Mat:............Density...........Specific Heat...........Conductivity
..................(kg/m^3).........(J/kg*K).................(W/m*K)
Stainless.......8000...............460.......................13.5
Carbon S.......7800...............470.......................43
Cast Iron.......7200...............420.......................52

Densities are a wash, but cast iron would be the lightest
Specific heat is a wash, but cast iron takes the least amount of energy to heat it up
Conductivity is interesting though, stainless steel is going to "hold" it's heat the longest and will take the longest time to get hot. Cast Iron will heat up the fastest and will also let go of its heat the fastest.

Conclusion (IMHO):
If you want to have quick (or quicker) changes in the temperature of your drum (i.e. one temperature ramp to another temperature ramp) and you have good control on your heat input, then cast iron would be the best choice.

If you want to have a consistent temperature (or temperature ramp) with only modest changes in slope, or you have poorer control of your input heat, then stainless steel would be a better choice. This is due to the fact that the stainless steel will not fluctuate as much as the other material (given the low conductivity) as the heat source changes (Q).

That's why they don't make stainless steel brake rotors...once they get hot, they stay hot...

Not from an engineering point of view, but from meat browning point of view, which is also a Maillard reaction. The meat browns better on a cast iron pan compared to stainless steel. I vaguely remember reading about this food science a while ago, but could not find the source.

kocurekc wrote:That's why they don't make stainless steel brake rotors...once they get hot, they stay hot...

The majority of all OEM motorcycle brake rotors are stainless steel.

JohnB. wrote:The majority of all OEM motorcycle brake rotors are stainless steel.

With lots of holes in them for cooling. I wonder if bikes use stainless because of exposure?
Most car rotors are solid and smooth carbon steel.

kocurekc wrote:Good engineering thought problem here...which material is best?

Great post.
Apparently you think like an engineer (send your wife my most sincere sympathies )

JonR10 wrote: With lots of holes in them for cooling. I wonder if bikes use stainless because of exposure?
Most car rotors are solid and smooth carbon steel.

Nobody wants to see a rusty brake rotor on a motorcycle but the modern stainless rotors work extremely well. Most brake companies like Brembo, EBC, ect use a proprietary stainless blend which works as well as the older cast iron rotors. Check out the braking times on the current crop of 180hp sportbikes.

Automotive rotors are typically cast iron but there are some aftermarket stainless rotors.

Now I want a Brembo drum. With red calipers!

I just checked (with a magnet) to make certain, as I remembered my Ambex has a stainless drum, & indeed it does. I would suspect they chose not to use carbon steel for a reason, as certainly the stainless is more expensive. What material does the Quest M3 use?