I've had my Monolith Flat since the first production run, and honestly I haven't found a use for variable RPM -- until now.As reported in another thread
, while on vacation in NYC I picked up a bag of Apes and Peacocks Zambian natural SO from Underline Coffee in Chelsea. I tried a shot of it at the cafe, and while it was rather under-extracted, I could taste some interesting potential, confirmed by blueberry notes when I sniffed a bean sample offered by the barista.
When I opened the bag at home, six days after roast, I immediately noticed that the roast was ultra light and there wasn't much aroma -- certainly not what I smelled from the cafe sample, which was probably from an earlier roast. What really blew me away, however, was that my Kafatek Monolith Flat couldn't grind it fine enough. This was a first for my beloved Flat, which I've owned since the first production run and recently upgraded with SSP burrs. I've never gotten close to the finest grind the Flat can do, so I was astonished when I got a gusher with the grind setting just barley coarser than the point where the burrs touched.
To be fair, I've been pulling singles exclusively for some time now, so the low dose was clearly part of the problem. I boosted the 8.5g dose to 17.2g in an 18g VST double basket. That helped a lot, but the shot still ran too fast, barely 25 seconds -- nowhere long enough to extract the ultra light beans properly. The shot was similar to what I tasted at Underline, so I figured the roast would push the limits of any grinder, and resigned myself to letting the beans rest at least a week longer before trying them again.
But overnight it struck me that there could be another solution -- bump the Flat's RPM! I've been running the grinder at 450 pretty-much since I got it, and have never played with different RPM settings. So this morning I set the Flat to 800 RPM (still the finest possible grind setting) and let it rip. Sure enough, the flow rate slowed way down. In fact, it was a bit too slow, over 50 seconds. The shot was still tart, yet much more drinkable, but no fruit flavors survived the long pull. I dialed the Flat's RPM back to 650 and that lowered the shot time to about 40 seconds, where the fruit flavors started to emerge.
Personally, I think the roast is just too light, but it's possible there'll be some improvement after letting the beans rest. I'll report back if there's any change.
For me, the takeway is that there really is value in having a grinder with variable RPM -- even if it took three years for me to find a use for the feature!
[Afterthought: While writing this it occurred to me that another solution would be to dig up one of my older standard double baskets, which should have smaller/fewer holes than the VST 18g basket.]