So I know I've railed against overly prescriptivist training in the past, swore that there's not a right way, and that we need only apply principles in ways that work for us. Well, this is a nice ideal, and I mostly stand by it. But just because there's not a right way to do a thing, doesn't exclude the possibility that there can be very wrong ways. I've seen too many of those recently, so I'm going to lay out my how-to-tamp guide.
Yes, this is going to be a little inside baseball for some. But at least I'm sticking somewhat to my profession, and not tangenting on my hobby (though there will be more racing posts in the future). So ok, tamping. Tamping is that thing were you press the espresso in to a puck, so that the water can extract the juicy goodness from it.
First, let's talk principals. You want the whole thing to be uniform, since water will cheat if it's not. For that same reason, you would really like the puck to be level. But that's not really so complicated. We need a flat puck with no holes in it. Pretty simple. But for something simple, the act itself often ends up mess, sloppy, and worse, fails to achieve the perfect puck.
I think this is caused, not by too little effort, but by too much. People get hung up on hitting some poundage with their tamp, and so they mash the whole thing, pressing down so hard that they lose feel for how the puck is compressing. Which really, is the opposite of what you want, keeping the principles in mind. You want a flat, uniform puck, and so you press down evenly, just hard enough to get that. Once it's solid, you can stop. Focus, not on mashing, but on pressing evenly and just hard enough.
Some people stop here. I think that's fine, but we're going to continue, because most people do. This is the part were to tap the edge of the portafilter, dislodging lose grounds. Again, it helps to keep the goal in mind. We want to knock the lose grounds away from the edge, not dislodge the entire puck. So tap just hard enough to do the former, and not the latter.
Of course, even a soft tap will move things around a bit, and remember, we want a uniform puck. So, we're tamping again. Some insist that this should be lighter than the first tamp, some say stronger. I say not to worry about it, and again, to press just hard enough. If that sounds too vague, it isn't. "Too hard" is something you have to feel for yourself, and if you're taking the time to feel what you're doing, you'll usually avoid it anyway.
Next, we polish. Or rather, some do. Ideally, this is supposed to smooth out the surface of the puck. However, if the tamps were solid, this probably isn't necessary. Still, if we're going to do it, let's do it right. And that means, as in the other steps, that we won't do it too violently. It's called a polish, after all, not a mash, and not a grind. Don't press down with your full body weight and twist the tamper back and forth, ruining the perfect puck you just made. Do, if you do anything at all, twist lightly, quickly, and not too much.
The last step is difficult to screw up, but too often skipped altogether. No matter how perfectly you did the other things, there will be lose grounds on the edge of the portafilter. We don't want those, so flick the portafilter, and run your finger around the edge. Failure to do so won't ruin this shot, but it will gum up your group head, which is gross, and can hurt the quality of future shots. Finally, before locking the filter in to the head, flush. This cleans out whatever mess you may have there, and optimizes the temperature.
That, basically, is it. We want a level puck, with nowhere for water to cheat around the grounds, and to not beat shit up in acquiring it. We want the process to be neat, controlled, and clean. Do that, and you get what we really want: Sweet espresso.