Over the past decade, making an espresso has become more and more of a scientific process. It's not uncommon for baristas to use scales to weigh out coffee doses and yields, measure out their espressos to the second, and make sure their water temperature is just right.
The goal of all this fiddly accuracy is to make the whole process more consistent by taking human judgment out of the picture. Don't estimate how much coffee you have in your portafilter but weigh it. Don't use your eyes to estimate when to stop the espresso but measure the time.
But there is one step in making an espresso that has retained its status as a kind of dark art: tamping. Tampering is one of the most beautiful tools you'll find at a bar, and many baristas consider tamping an important part of their craft. It can be one of the most daunting parts of espresso preparation, but it doesn't have to be that complicated. It's basically a very simple process, so let's break it down.
Goals
The goal of tamping is to press the ground coffee into a flat, even puck through which the water flows smoothly. Ideally, it should be perfectly flat and have a uniform density. It should not be so tightly compacted as to impede the flow of water, and not so loose as to create gaps or cracks through which the water can pass - also known as channeling.
Approach
Hold the tamper like a flashlight, that is, with the tip pointed down at the ground. Grasp the handle with your fingers, and point your thumb at the base of the tamper. When tamping, try to have your elbow pointing vertically upward as an extension of the handle. Your wrist should be in a neutral position, and there should be a straight line from your elbow to your thumb. This will ensure that your body weight is applying the force and not your fingers or wrist.
Pressure
Bring the base of the tamper to the surface of the ground coffee. Pause for a moment to make sure everything is level and straight on all axes. The goal is to press the tamper into the basket like a piston - it should move smoothly and straight down into the coffee bed, compacting it evenly.
How much?
Unfortunately, it's hard to say how hard to press. Not too hard and not too gently. If you use your body weight properly, you shouldn't have a hard time applying the necessary force. Often people instinctively tamp too hard, which can lead to an uneven puck and thus uneven extraction. So, start gently.
Removal
The last point to consider is how you pull out the tamper. A tightly fitted tamper can create suction if pulled out too quickly, which can pull the coffee puck out with it. Pull it out carefully, being careful not to ruin your hard work.
Want personal coaching on your tamping skills and the whole process of making espresso? Attend a barista class at the roastery to get trained.
