Pressure is what makes an espresso an espresso. I don't mean the kind of pressure that caused you to start smoking in high school: I mean a combination of the pressurized water coming out of the espresso machine, as well as the resistance caused by the perfectly packed cake of coffee grounds the water has to push through in order to brew.
Today, we'll explore a contributing factor to this perfect storm of pressurized extraction: the tamper.
Why We Tamp
Tamping is the method a barista will use to take a loosely dosed amount of coffee grounds and turn them into a tightly compressed, evenly dispersed puck within the portafilter, where the water and coffee will come in contact when it's brewing.
Why is it necessary? For one thing, the espresso needs to be compacted far enough to create a little space between the top of the coffee and the screen through which the water comes out of the espresso machine. Once the coffee grounds get wet they'll naturally swell a bit, which can cause a sludgy mess without a proper gap.
The other main reason for tamping is that water is lazy. It doesn't want to have to do the hard work of pushing through that coffee to extract all the deliciousness inside. The only thing lazier than water is water under pressure, and if it's forced through a loose pile of grounds, it will inevitably find all sorts of cracks, crevices, and channels to zip through, avoiding all the good stuff we want it to absorb from the coffee. But if those grounds are tightly pressed into a level cake, the water has no choice but to squeeze through it evenly, picking up all kinds of flavor along the way.
When you're ready to tamp your espresso, you'll want to make sure you do so in a way that's not going to hurt you over time. It might sound silly, but repetitive strain injuries are a reality for baristas—not to mention a real bummer. (I've definitely had to wear a brace before, on account of poor form.)
Be sure that when you push down on your tamper that your wrist is perfectly straight, and your elbow is bent at about a 90° angle. You should feel the pressure coming from your shoulder and triceps, and the force should not feel like it ends on your wrist joint.
And never apply the weight until you're sure the tamper is resting level in the coffee bed: An uneven tamp means an uneven extraction.
How Hard Should You Tamp?
The question of how much or little to tamp is a big one for new baristas, and I say don't sweat an actual amount of "poundage." I mean, if I tell you to put 30 pounds of pressure on your coffee puck, are you honestly going to know what that means? Similarly, no one thinks you're a tough guy if you tamp with 100 pounds or more, I promise. (And leave the bathroom scale in the bathroom: We're making coffee here, not checking in at Weight Watchers.)
Instead, work on achieving a consistent amount of pressure—whatever it may be for you—and try to ensure that you re-create it every time you tamp a shot into submission. Consistency is always key. If you need to make any adjustments in order to speed up or slow down your extraction (which should last between 20 and 30 seconds), don't change your tamp pressure: Instead, make the grind size of your coffee coarser or finer (respectively).
The Right Tool
Tampers come in all shapes, sizes, colors, and weights. Just as the wrong bowling ball can send your rolls into the gutter over and over, an ill-fitting tamper can cause wrist injury, callouses, and generally be a regular nuisance.
If possible, get up close and personal with as many styles of tamper as possible. Feel their weight and contour in your palm, and apply pressure against them on a counter or table to see how they feel when put to the test. For home users, tampers are pretty easily found at specialty markets like Sur La Table, and are also readily available online at places like Whole Latte Love. The latter sells a range of quality products, from weight-calibrated units, to classy rosewood-handled pieces, and inexpensive models suitable for more casual users.
You'll want to double check the circumference of your portafilter basket: Tampers generally come in sizes from 56 or 57mm to 58 or 59mm, and you'll want to make sure that whichever one you buy will fit without sticking. (Erring on the smaller side is okay, you may just have to tamp more than once to compress all of the coffee.)
Do you have a preferred size, style, and model of tamper? (Confession: I have one with my name engraved on it. Also? It's Sooner red. Boomer!)