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.