A barista at my favorite local coffee shop (before the owner sold out and it became a wine bar, and the Synesso & Mazzer's are now being used with canned Illy) used to store his tamper on the Synesso cup warmer, the idea being it wouldn't shock the grounds which were warmed coming out of the grinder. This was kid serious about his espresso. He would often dump out a dopio he pulled for me as wouldn't be just right, and did weekend espresso bar crawls checking out the local coffee scene.

One, it's a convenient place to store for me, but as to the effect on the coffee..? I know I don't have the palate to taste the difference. What do you think - help, hurt, or hyperbole?

Yeah the coffee sitting in the hot portafilter basket is going to care about the warm tamper

/sarcasm

That sounds a bit unnecessary to me. I can't imagine that the amount of heat or cold conducted from the tamper to the grounds would be enough to "shock" the grounds and affect their flavor. Maybe if you kept your tamper in the freezer, it would be cold enough to make a difference, but even then I doubt it would change the flavor in the cup.

.... not to shock the coffee? Seems like an odd thought to me, given the miniscule amount of contact a tamper makes with coffee, even when heavily compressing it. Heat transfer is primarily a product of time and thermal conductivity. The time is minimal, and coffee is most certainly not a conductor (indeed, with the amount of air in a dry puck, it's quite the insulator). In any case, I believe that coffee exits the grinder chute at usually no more than 80-90F, maybe somewhat more than this in an extremely busy cafe. Assuming it's around 70F at room temperature, I'm confused why you would ever thing that a tamper at that temperature would affect the puck more than one that's been sitting on the cup warmer. I insulated my Elektra's boiler, and it's still around 135-140F on the top of the cup warmer (checked with a Fluke ) I wouldn't be surprised if a Synesso/LM with a steam boiler rocking 1.5 bar, not insulated, is even hotter than that up top. I don't know why one would expect such a hot temperature piston would be less shocking to the coffee than a room temperature one, not to mention 2-5 seconds after you tamp, when the water is hit with ~200F water at 9 bars of pressure.

Anyway, that's entirely more thought than the issue likely deserves. This is most certainly a superstition.

Which is not to offend or berate your barista friend, Eric. I am sure he makes a fine cup of coffee. Attention to detail is a plus, but even the best of us get caught up doing strange, ultimately pointless things with the idea that they improve results in the cup.

My money is on odd superstition.

When will someone start touting the health benefits of magnetic tampers?

I've been digging my lead tamper with asbestos handle, actually.

Not to mention that, if you are not careful, some coffee debris can fall into the warming holes on top of the machine, creating havoc on the internals.

OK, so I realize that a little coffee grinds falling through the ventilation holes on the cup warmer can make the machine dirty, but 'havoc?' Really? That seems a tad dramatic to me.