Convex vs. Flat Tampers

Searching through one of my utility drawers, I discovered a small black plastic tamper. Interesting, I thought. Now that I’m spoiled using the La Marzocco Swift Grinder this is like an ancient relic reminding me of the precision, accuracy, and skill of my forebears. But it isn’t like the tampers I used in the past… it has a convex tamping surface. This set me on a series of questions to find out which was better (and as I found out for what each was better suited). I put my question into google and searched through boards like home-barista and model comparisons from coffeegeek (though I found that he does a mid-tamp tap, which makes the entire article suspect). I was surprised that a majority of posts were in favor of the convex tamping surface. Here’s my take on the results:

The tamping process crafts the puck and exposes channeling through the espresso. The convex tamper design is helpful in a few different cases, primarily when dealing with the pf basket. Portafilter baskets can apparently be crafted with a slightly convex base as well, making an even tamp possible only with the convex tamper. It can also be an aid for baristi who find that the outside of their pucks are prone to channeling or “weeping” (the outside blonding during the pull) as the convex nature seems to push grounds towards the outside, creating a better seal.

The counter argument says that the convex tamp funnels water through the middle of the puck leading to under-extraction on the outsides. A flat tamper model receives the water right off the group at an even rate extracting the 7-8 grams perfectly over the shot time. This does require a greater attention to leveling the puck pre-tamp, but even the case of a convex tamper correct dosage is also a must which is best accomplished through proper leveling.

So if my options are between under-extraction and the need for greater precision, I would side with the flat tamper, so long as my grouphead screen and pf basket are not obviously convex.

What’s this thing doing in my drawer?!