Suspecting that worn burrs were preventing me from getting a fine enough grind, I got new burrs from cmc espresso for my la pavoni zip grinder. Various coffee forums on the internets contain advice that recommend that you replace burrs if you can’t get a fine enough grind with a good grinder.
From my experience so far, that appears to be good advice. With the finest setting for each set of burrs (as fine as you can go before the motor stalls) I went from pulling a decent espresso shot with 21g (with a triple basket) to having an way overextracted 15g shot. I still need to do some tweaking, but it wasn’t possible to overextract at all with the old burrs.
Here’s what came in the mail, and here’s how the burrs compared:
and here’s the direct comparison:
I recall reading in some forums that you can tell that burrs are dull if the leading edges look shiny. That appears to be the case in the above image. Note that on the left side old the old burrs, the leading edge (top edge) of the flat part of the burr appears to be shiny.
The new burrs themselves look to be lower quaity than the old burrs. There are lots of little burrs (ha) on some of the edges and the finish on the other parts (due to casting? I am not sure how they’re made) isn’t as nice. The coffee probably won’t notice though.