Even with first-class espresso beans and the best equipment in the world, an espresso can taste watery and sour if mistakes are made while tamping the coffee grounds. Even the smallest mistake in tamping has a surprisingly large effect on the taste and can make the difference between a delicious cup of espresso and a cup that has taken a long time to prepare but is ultimately poured down the drain. How the tamper is pressed onto the coffee powder is, therefore, decisive for the quality in the cup. We will explain what you should consider when tamping properly.
What is a tamper?
A tamper is a small plunger that has a smooth or a convex (slightly curved outward) metallic surface. The diameter of the tamper should be the same as the sieve insert. So if your screen is 58mm in diameter, you should use a 58mm diameter tamper. A tamper is also known as a coffee stamp or coffee press.
Why proper tamping is so important.
Tamping refers to the compression of the ground coffee in the sieve insert into a firm, uniform “coffee cake” with a smooth and even surface. This counter-pressure surface on the coffee grounds is required to offer sufficient resistance to the water that flows out of the espresso machine at high pressure (approx. 9 bar). The tamped and solid ground coffee surface is therefore responsible for building up the desired pressure during the espresso extraction.
We can recommend this tamper from Motta:
Prevent channeling through proper tamping
Tamping aims to compress the ground espresso straight and at the same height in the sieve so that the water can move evenly through the espresso. This is especially important so that the so-called “channeling” is prevented. “Channeling” describes the phenomenon that water always seeks the path of least resistance.
If the ground coffee is unevenly distributed, the water first makes its way through a few channels. As a result, more channels are added, but the extraction is uncontrolled, intermittent, and uneven. If you tamper at an angle, the water will flow through the thinner part of the coffee puck, preventing the even extraction of all of the coffee grounds.
The result: The espresso tastes under-extracted (sour & watery.) It has little body and a flat aroma profile.
Here you can find out six other reasons why an espresso tastes too sour.
You can recognize the water channels created by the channeling in the form of cracks after you have taken them in the coffee puck. So you have proof that obviously, not everything went right. We, therefore, recommend that you practice proper tamping. It is helpful to screw a screw into a wooden board with a screwdriver. This trains the correct hand position of the tamper.
Tip: If you are unsure how to proceed with espresso preparation, we strongly recommend that you read our extensive guide article on the subject of espresso.
This is the right way to stamp
Find out below how you should proceed step by step when tamping properly.
Place the portafilter filled with leveled coffee grounds horizontally on a tamper mat or place the portafilter in a tamping station.
Place the tamper vertically over the portafilter. Due to its weight, the tamper sits flat on the grist. Check the vertical position.
Hold the tamper like a screwdriver with which you want to tighten something from above. The hand and forearm are in a straight line. Now build up a vertical contact pressure of 15-20 kg on the coffee grounds. It doesn’t matter whether you build up exactly 15-20 kg of pressure. Above all, the surface of the coffee grounds must be smooth and firm. And you can do that if you press down on the coffee grounds with the tamper.
Reduce the contact pressure a little and turn the tamper by approx. 120°. This “polishes” the surface of the coffee grounds and smooths out any unevenness. The result should be a firm, smooth, and level coffee surface.
Finally, you have to clean the edge of the portafilter from the coffee grounds with your finger so that coffee grounds residue does not scratch and damage the seals on the brew head.
Before you start tampers, you should level the coffee grounds properly. In our opinion, correct leveling is much more important when preparing espresso than tamping. Therefore, you should also deal with it.
Tip: Do not hit the edge of the sieve after tamping
Powder residues may have deposited on the inner edge of the sieve after tamping. Inexperienced baristas hit the edge of the sieve with the tamper to send the remains from the edge to the center of the sieve. We cannot recommend this procedure and you shouldn’t recommend it, as well because it will detach the compressed coffee cake from the wall of the sieve and sometimes cracks may appear. During the espresso extraction, the water will shoot through these cracks first. This prevents coffee grounds from being extracted evenly. The result is an under-extracted espresso.
Proper tamping is important so that the espresso extraction can run perfectly. Only with a firmly tamped “coffee cake” with a smooth and even surface can a counterpressure surface be built up that offers sufficient resistance to the water. Above all, be sure to tamp straight so that the ground coffee surface is absolutely flat. Only then can the entire coffee grounds be extracted evenly. In this way, all valuable aromas are released from the coffee.