Gwilym Davies says it best: “Tamping is very, very simple.” It’s a part of espresso making that offers plenty of opportunity to mess up the coffee but nothing much we can do to improve it.
Why do We Tamp?
The commonly given reason for tamping is to break up clumps and press out air pockets, to prevent the water from finding shortcuts through the gaps and creating channels. However, it’s possible in some circumstances, provided the distribution is perfectly even, to make good espresso without tamping — instead, the water pressure from the pump compresses the puck. For example, some users on Home-Barista.com advocate not tamping at all. Similarly, 2009 World Barista Champion Gwilym Davies reports that he once was forced to make espresso without a tamper when he appeared on an Australian TV show. “A stagehand had moved the tamper, as it was in the way … but [the shot] came out beautifully after I vertically tapped it lots of times.” His experience suggests that good distribution can sometimes effectively replace the function of tamping.
One factor that makes tamping necessary, however, is the effect of water hitting the coffee or any other factors that can break up the coffee bed before brewing. A tamped bed is more likely to resist the impacts from the first drops of water or from the portafilter hitting the machine, for example, whereas a loosely packed bed of coffee produced by distribution alone can be easily disrupted. After his experience on Australian television, Gwilym tried the tamp-free technique at home with his Athena Leva machine. “We tried it without tamping and it was terrible,” he says. “The piston going up causes a vacuum … and disrupts the puck when the lever is pulled down.” A tamped bed is more likely to hold its shape.
Tamping is also the quickest way to get a perfectly level bed of coffee so that water has the same distance to travel,