Since I have Giotto (and no money left at the moment for a proper tamper) I've been using old tampers which are way to small for the Giotto. What I need is a 58mm tamper (which I had once, but gave to my friend who bought Silvia from me...).
So here I was, tamping with whatever I could find in the house which had some sort of the size and flatness I needed...
I was getting pretty desperate as nothing seemed to work... So I went for the fridge and took a beer...
I tried the bottom of the beer-bottle, and you know what..?
It fits almost exactly, and the grounds are tamped in a slightly round way as the bottom is a little bit 'hollow'... The shot's are great and I think now I have discovered a new thing to get a patent on... The round/heaping puck in stead of the hollow-puck which should match curved filterbaskets.
In fact I think that a slightly-heaping-tamped-ground which rounds a bit gives more resistance to the water (round is stronger than flat) and as most pressure is in the middle of the grounds, it's a good thing to have slightly more coffee there... (this should apply only to flatt filterbaskets)
But I'm not a scientist, only enjoying a discovery which probably (if I stay content with it) saved me 35 euro...
Michel