Can't fool mother nature...

... but you can fool me pretty easy.

My Aillio Bullet R1 roaster has a device built into the front plate that allows the operator to take a look at the beans during the roast. It's a little tubular scoop that can catch a few beans as they crash around inside the drum. Gives the operator a chance to see the bean color and get a whiff of how the roast is progressing, It's called a 'tryer' and it's pretty slick.

Recently I've been playing with drum speed. Drum speed wasn't adjustable when I first got the Bullet (it should have been). When I upgraded the power board to V2 (and the control board as well; my Bullet is now a V2 Bullet) I suddenly had control of drum speed.

At the suggestion of one Bullet owner, Glen Junkert, I started using a lower drum speed at the start of the roast (D4) as part of something Glen calls a 'heat soak' prior to increasing the power to get to roast temperatures. Midway thru the roast I start increasing drum speed as the roast progresses so that by the time I get to 1C I'm at D8.

Here's where mother nature enters the picture (or Classical Physics if you don't feel that spiritual). When you lower drum speed, the path of the beans inside the drum is altered. At lower rotational speeds (lower Drum speed), the beans separate from the drum wall earlier. Makes sense that at lower drum speed there is less centrifugal force to hold the beans against the drum wall so they fall away sooner. Being a skeptic you interrupt and ask "well... so what?" Well, if the beans separate from the drum wall sooner that means the beans miss the catch zone where the tryer is located, ergo no beans in the sample. The diagram shows how the beans follow a different path determined by drum speed (copied from CoffeeNavigated.net, a really fascinating site for tech-heads that own a Bullet).

Sadly there's no way to fix the issue since the tryer location is fixed by a tube welded into the face plate. Mother nature says beans fall to the bottom of the drum at a certain location based upon drum speed and the mass of the individual beans. If you change drum speed you change where those beans fall away from the drum and land on the other side. Can't fool mother nature! For that matter, you can't fool Sir Isaac Newton either.

And in case you're into such things, here's the calculation that determines what drum speed is needed to keep the beans against the wall of the drum. Ideally you would operate the drum at about 75% of this value to guarantee beans don't get pinned against the drum which would likely burn the beans (called 'tipping'). Again, from CoffeeNavigated.net.