You’re a barista. Maybe at home, or maybe you’ve been working in a shop, and you hear all sorts of theories about how to tamp your espresso, ultimately deciding that how you tamp, doesn’t really matter that much. I’m here to tell you, that it matters a great deal, and the reason is not among the most popular theories!
Here’s a little background. When I first learned to pull shots, the “rule of thumb” was to create an even tamp with 30 lbs. of pressure. Most people don’t know what 30 lbs of pressure feels like, so it’s good to train yourself by tamping onto a bathroom scale until you are familiar with the amount of strength it requires.
Over the years, however, I have seen baristas set the tamper on the portafilter and give it a little press and a twist with their fingers, just to even off the top. Or worse, use that plastic convex tamper that is attached to the front of some commercial espresso grinders. Someone should go around with a hammer and break those darn things off!
Here is the deal. It all comes down to evenness of extraction. The more even your extraction, the higher level of extraction you can achieve without diminishing the strength of your espresso. Under-extracted coffee tastes sour. Over-extracted coffee tastes bitter. If your portafilter and tamper does not present an even depth because the filter is contoured on the bottom or your portafilter creates a concave impression in the top of the puck, then you are going to get uneven extraction. The thin spots in your puck are going to be over-extracted or the thick parts are going to be under-extracted.
The same happens when your puck is not perfectly level. When you tamp an espresso and your tamper is leaning a little to one side, then you have created the same conditions that lead to over-and-under extraction.
Now, let’s visit tamping pressure. All grinders produce a less than perfect grind. Some grounds will be larger, some will be smaller. This is the major criticism of blade coffee grinders—they offer no consistency. But even the best burr grinders are going to have some amount of variation in the size of the grind when you take it to a microscopic level. The reason this is important is because smaller coffee grounds will reach maximum extraction sooner than larger coffee grounds, so you are going to over-extract your coffee, based on how inconsistent your grinder is.
This is the brilliance of espresso! By using a machine where you control the water temperature, the brew pressure, the amount of coffee, and the volume of water used for extraction, you arrive at a precisely controlled and consistent result. But what about the inconsistency of the grounds? That is solved through tamping pressure! The ancient Romans learned that they could build solid roads by fitting smaller stones between larger stones, creating a more durable and consistent surface when the stones were compressed. This idea may well have come to mind when the Italians invented the espresso machine, as compressing ground coffee into a puck will squeeze out the air between the coffee grounds, making a consistent mass, and resulting in a more consistent extraction because even though some of the coffee fines are in the puck, compression turns all of the grounds into a solid mass and the water now has to go through the mass of coffee grounds, creating more even extraction.
So, to maximize extraction and strength without sourness or bitterness, make sure you tamp your coffee with enough pressure to remove all voids. The first rule of thumb is that you cannot over-compress. That is why 30 lbs. is a good benchmark. Trust me, you cannot get 30 lbs. of downward pressure with your fingers. You have to use the palm of your hand and you should feel your bicep tighten. Then look at your surface, eyeing it against the wall of your portafilter to make sure it is even all the way around. if it is crooked, knock it back into the doser and start over. There’s no waste, and no excuse for a less than perfect tamp. Your customers will appreciate the extra care because it will make their drinks taste better!