Hand grinder burr alignment, and what the paper test showed
My hand grinder, a budget steel conical burr model, had started producing an odd grind: a lot of fines at a setting that should have been medium, with espresso shots that channeled unpredictably and pour-overs that stalled. I assumed the burrs were wearing. They were not. They were misaligned, and the test that showed it cost nothing.
The paper test: take the grinder apart, clean the burrs, reassemble, then tighten the adjustment until the burrs just touch and you can hear them rub when you turn the handle. Then take a thin sheet of paper, rub pencil graphite across a small strip of it, and wipe that strip around the inner edge of the outer burr. Tighten to touching again, turn the handle one full rotation, and open it up. Where the burrs touch, the graphite is wiped off. If the alignment is good, the wipe is even all the way round. Mine was wiped clean on about a third of the circle and untouched on the rest.
The cause, when I looked closely, was a tiny ridge of metal and old coffee oil on one of the three seats where the inner burr’s carrier sits. A toothpick and a bit of alcohol fixed that. Reassembled and tested again: the wipe was now even around maybe three quarters of the circle, with one spot still light. Good enough to try.
Results. The pour-over at my usual setting went from a 3 minute 40 second drawdown with a stalled bed to 2 minutes 55 seconds with a clean flat bed. The fines ring on the paper was visibly thinner. The espresso improved more dramatically: the same dose and setting that had been giving 36 g in anywhere from 22 to 38 seconds settled into 29 to 32 seconds over six shots, and the ugly spraying from one side of the bottomless basket stopped.
I had been about to buy a new grinder. Instead I spent twenty minutes with a toothpick and a pencil, and I now do the paper test every time I deep-clean the burrs, roughly every two months. One caution: do not run the burrs touching for more than a turn or two, and do it with the grinder empty, because steel on steel without coffee in between will chip the edges.