For those of you who can adjust the drum speed. I know Rao is suggesting increasing speed toward the end of the roast but Boot suggest to decrease the speed at the end of the roast. Anybody tried the different options and found any difference?

Ridiculous IMO....leave the drum speed at whatever is right for the roaster.

DaveC wrote:Ridiculous IMO....leave the drum speed at whatever is right for the roaster.

If the drum speed is adjustable, how do you determine the right speed for the roaster??

Beans expand during roasting. The have a greater volume as they swell 35-45% during the roast. At the end of the roast, depending on the bean, I will bump up the RPMs for less prolonged contact with the drum and a bit of agitation to compensate for the increased size.

I am unsure why you would slow the RPMs unless he is suggesting the beans weigh less and he is using air as a complement to agitation. I have never slowed the drum at the end of a roast.

Chris Schooley had the same discussion thread few years ago in the roasters guild forum. In that thread, Marty G Curtis raised the "caution" flag when one tries to compare various types of roasters in a blanket statement. http://forums.roastersguild.org/viewtopic.php?t=38

I don't have Rao's book at hand now, but can double check it when I get back home. IIRC, Scott considered drum speed the least important variables amongst other factors. On a table showing suggested initial drum speed for different capacity roasters, it is very narrow range (e.g. 52-54 rpm; this is only 4% difference). In other words, if you have variable drum speed roaster, (usually) the rpm can be slightly increased with the progression of a roast, and the effect would be similar to (but much less pronounced than) increasing the airflow.

At least it's my understanding.

That is also my understanding but I was wondering about the completly different suggestion by W Boot?

Does Boot give the reasons behind his suggestion?

Here is the link for the video:
https://coffeecourses.com/coffee-roaster-drum-design/

My roaster has adjustable drum speed. Here is how I've been using that feature, but I haven't done any very scientific assessment. On larger batch sizes I'll use a slightly higher drum speed to ensure sufficient agitation, but I don't change the drum speed throughout the roast. On smaller batches I use a lower speed. And for smaller batches, in particular where thermometry readings are potentially hypersensitive due to the reduced batch size, I tend to increase drum speed throughout the roast as a substitute for increasing airflow which would tend to cause large fluctuations in readings. Drum speed changes for small roasts are just a gentler way to increase convection.

Never heard of decreasing the drum speed later in the roast, so would be curious to hear the thinking behind that.

keno wrote: Never heard of decreasing the drum speed later in the roast, so would be curious to hear the thinking behind that.

See the link in my previous post for the reasoning.