JamesM over on 'that other place' mentioned recently that he'd abandoned polishing as he believed that it actually disrupted the puck and caused channeling. As part of my ongoing coffee evolution I've been experimenting with this recommendation.
And it's worked wonders. I've been enjoying my doppio ristrettos like never before. I'm getting vastly less (but still some*) channeling and a much better result in the cup.
*JamesM also (oddly) pooh-pooh's the idea of precision fitted tampers/baskets. As I have a terribly-fitted tamper, I have problems getting a level tamp and all my channeling occurs around the edges, so I don't agree. Although a Pullman and matching Synesso is greatly desired, it's way down the list of things that I can justify the purchase of to the finance minister!
Hi! Phew, I made it. How old is this thread? I have been experimenting with not polishing my grinds after tamping. Honestly, I think if you polish gently (no pressure) you are good to go, but if you polish with ANY pressure, you are basically screwing around with your nicely tamped grinds, possibly introducing issues. I've basically stopped 'polishing' all together, I am certainly not getting 'worse' results in the cup by avoiding it.. generally reducing channeling to some degree (from my own experiments)
I read an excellent thread on the home barista forum called "tamping twaddle", which goes in depth (including part #2) in to tamping with precision tampers, vs NOT. I'm convinced that a precision tamper isn't required to get good results. I do however believe that a precision fit tamper will assist you with getting a 'more' level tamp on your grinds compared to one that has a little slack. A precision tamper CAN cause a vacuum when swiftly removing your tamper from the grinds after tamping, pulling the puck away, you need to be quick to see it, sometimes it's minimal, but never the less, it's ruining your tamped grinds.
For me, it's about results in the cup. Some people polish, twist, knock, tap, swipe, do a little dance, grunt, whatever. Just make good coffee!