It is easy to rush the tamper, as the portafilter already looks full and ready to brew with fresh grounds in the basket while the espresso machine awaits. It seems obvious that after filling the basket and loading the portafilter, one should simply grab the tamper and press down, creating the foundation for brewing. But the coffee puck is developing before the tamper even touches the coffee in the basket. This few second period before tamping affects how water moves through the coffee evenly and where the water can more easily penetrate weak areas of the puck during extraction.
Check the distribution before tamping the coffee. If the coffee sits unevenly with one side higher than the other in the coffee basket, tamping will create a puck that is also uneven. When the grounds in one corner are more tightly packed than in another, water will not flow uniformly through the coffee, even if the dose is correctly measured with the scale. Before tamping, lightly settle the coffee and check the surface before pressing to create a more even puck surface.
An early exercise is to dose your coffee into the coffee basket of the portafilter, look at the distribution in the basket, then tamp the grounds and pull the shot. Do this several times without worrying about the taste of the brew. Look directly at the coffee in the coffee basket before tamping. Observe if the coffee looks mounded in the center, leaning toward one side, stuck together in clumps, or spilled on the rim. Distribute the coffee to more evenly fill the coffee basket, and look again. This exercise will get the barista to notice that the preparation of the coffee puck in the coffee basket is an important barista technique, rather than just a part of loading a portafilter to brew a shot of coffee.
Spilled coffee from the coffee basket should not be overlooked by the barista. Spilled coffee can prevent the portafilter from sitting in the group head in a sealed manner, which can be messy during the workflow. Wiping around the coffee basket and the rim before locking the portafilter in the group head is an important step for cleaning the area around the seal gasket, which helps the workflow feel more streamlined. This process is not about making the coffee basket look great for Instagram, but about cleaning up the small issues that can influence the espresso.
Tamping the coffee puck is best done after the coffee has already been distributed evenly. If the coffee is not distributed well before tamping, the barista is likely wasting time and effort as tamping harder will not correct the unevenness. Increasing the pressure during tamping can also make new brewers feel as though they have fixed the issue when channeling becomes visible in the shot. The goal of the tamper is not to compress the coffee into a hard puck, but to tamp down the coffee to make a firm flat surface to press after the coffee is distributed as equally as possible in the coffee basket for the even penetration of water flow.
After tamping the coffee and pressing down with the tamper, check the puck surface once more. The surface of the coffee puck should be flat, not sloping in one direction. If the puck is leaning, the tamper was pushed in at an angle or not kept stable and straight during tamping. By checking after tamping and tasting the shot of espresso made from this puck, the barista will start to connect what happens in preparation before tamping with the taste of the final shot. A sour and weak shot of coffee may not be about the grinding fineness of the coffee alone; an uneven distribution of the coffee in the basket or a hole in the puck can cause the sour shot as well.
Before tamping another shot, knock out the old coffee puck, brush the coffee basket out, dry the basket, and take the hands back rather than rushing through filling a portafilter. Taking a small pause to visually check coffee distribution before the tamper can make the practice of brewing espresso feel more intentional. By the time the basket is brushed and empty, the coffee is distributed, the rim is wiped clean, and the puck surface is leveled during tamping, the shot has a good foundation to reflect the flavor of the roast of coffee, grind size, dose, and yield.