Variable Drum Speed

[Musicphan]

Hi All -

I'm putting the final 'config' together on the USRC machine ... one of the options is a variable drum speed control. It's not terribly expensive but I wonder if its something that's even worth doing. I did a bit of research over the weekend and there simply isn't a lot of info on the good old interweb. Any feedback/thoughts/experience?

Mike

 

[chast]

I have a US Roaster with the Variable speed control and I never used it. Thought it might be good to have but.......7 years and never touched the factory speed.

 

[sae]

I could see using it only when doing very small batches

 

[ellatas]

Most manufacturers of drum roasters have determined a specific rotational drum speed that appropriately balances when the coffee is in the airflow and when it is on the drum and provides the best mixing throughout the roast. If the drum speed is too great, more coffee will stay on the drum wall throughout the rotation and not get into the airstream. Likewise if the drum speed is too slow, more coffee is not lifted up into the airstream.
The formula for the maximum drum speed is (30/pi).(g/r)^1/2 where g is the gravitational acceleration and r is the drum radius. All drum speeds should be below this figure.

 

[soliloquy]

As long as it's not too much of a premium (as in price) I'd say go for it. It can't hurt.

Maybe someone else can speak to this, but wouldn't it be beneficial to be able to manipulate the drum speed during a roast, as to compensate for the increase in volume as the coffee expands? If I recall, Scott Rao touches on this a bit in book, The Roaster's Companion.

I've also heard that Kickapoo turns their drum speed up later in their roasts in order to "float" the beans and achieve more of a convection/ fluid kind of heat transfer. Though I would think you'd have to be careful not to stick the beans to the drum wall.

I guess all this is to say, who knows.