I forget where I saw it above, I did want to add though that Espresso is not using steam to brew, it is using water, heated to somewhere between 195-205°F (La Marzocca recommends an even 200 as the starting point) at the group head. It is under pressure at a recommended 9 bars.
As for tamping to a specific density having an effect on results… certainly though I haven’t personally researched or seen a study on this.
More than anything, the goal is to create a uniform bed against which the hot water is “pressed” against. In an ideal setting, water is exiting the distribution or Shower Screen in a regular and even pattern, against a flat and level puck with no inconsistency to its structure, and passing through the basket with little resistance that could impede what should otherwise be an “unrestricted” flow (yes, there are restrictions to the flow, but here I mean that the basket itself is somehow NOT altering anything in the system).
Interestingly, it has been pointed out that the 9 bars of pressure an espresso pump should be delivering is far in excess of most people’s ability to firmly tamp the grind in the filter. So as I described in an earlier post, the real goal is simply to provide a consistent puck which will hold together on its own and not break apart.
I always give a gentle spin if my portafilter. Habit really, but cool show off technique. If the grind doesn’t stay put, you failed at your task as a Barista.
@highfigh , I think it was you that commented about brewing a pour over with some tamping pressure applied. I learned early on to stir (first add a little hot water to bloom the grinds, then pour in to fill the cone and stir the grounds). I’ve since seen other techniques, too.
In the end, I think this just comes back to determining what works on the individual level and the only limit is how far you are going to go for consistent repeatable pours. In a coffee shop obviously you want it to be the same day after day. At home?… as long as you enjoy it you did good.
