ChrisC wrote:Think about it, it's just like pulling the plunger back on a needle to draw blood. The air needed to fill the gap between the tamper and the edges of the basket has to come from somewhere -- if you pull fast enough, it needs to be a lot of air fast, and there are all those little holes at the bottom of the basket...

Do you tamp with wet coffee? ground coffee is quite porous, and lever espresso machines draw air through it (packed) every time they are used (unless you draw the piston up prior to locking in the basket). It is, in fact, not like pulling a plunger back on a needle to draw blood: nothing in that equation is porous like coffee. I suspect that that the loss of adhesion you experience drawing the piston up comes from something else in what you're doing.

I've never owned a tamper that fit the basket so tightly it could be used as a syringe, but if you use a bottomless portafilter, you can hear the air being pulled through the puck during the upstroke on a lever machine. I keep the portafilter just short of snug until the piston approaches the port for filling, then snug it down. Once the puck is saturated, you can see the espresso on the bottom of the basket being sucked back in during the upstroke. A smooth lever action will reduce the impact to the puck's integrity, but the flow for the second pull is always faster because of the fissures caused by the upstroke.

ChrisC wrote:Hmm, good point about coffee being porous -- I just assumed that when it was tightly packed it wasn't quite porous enough... Maybe I was using a finer grind, or tamping harder than you...?

Do you think you could take some pictures of what your broken pucks look like? That might be helpful for us. I have trouble believing that you could be tamping that much harder/grinding finer than anyone else--if it were that significant, you would be choking your machine to death.

My first thought would be that a tight fit makes it hard to pull the piston out properly, and if you're not careful, maybe you tilt it as you pull up? That's just my off-the-wall guess.