One of the reasons that led us to write about this topic to launch the blog is the variety of pressing or tamping techniques that we have observed in different cafes, or between different workers at the same establishment. Also because of the different conceptions that people have about this action when they ask about it. It is one of the most iconic operations in the barista world and there are a number of reasons why a good pressing is crucial.
Once the coffee is ground and distributed inside the cup, any air pockets that may have been trapped between the coffee particles must be eliminated, preventing the water from passing through some areas more easily than others and resulting in uneven extraction. . In this way, the coffee is prepared so that the discharge and passage of water is homogeneous throughout the entire product. Only in this way will we have a uniform extraction espresso after espresso, and we will minimize the tunnel effect to obtain sweeter drinks.
With experience and tactile memory, we will also end up knowing if the grinding point we have obtained is adequate and if the distribution and distribution of coffee in the cup is uniform.
A good pressing.
Knowing that the objective of pressing our coffee is to seek a homogeneous extraction, it is easy to understand that the best tamping is one that is completely level. Tapping with the tamper on the sides must be avoided, as it can open cracks in the perimeter that are difficult to seal with a second pressing.
A good technique that is personally effective for me is to place the index finger and thumb on the edges of the tamper, while with the rest of the palm of the hand I push it down. This way I control that both fingers enter at the same time and the tamper is level. Another useful tip is to make a 90-degree angle at the elbow, to avoid injury and to exert as much vertical force as possible.
When removing the tamper from the bucket, it is important not to hit the sides and do so gently so that, if there is little tamper/bucket clearance, cracks do not form due to suction. Turning the tamper when finishing is a flourish that can be avoided.
How much force do we have to use?
We enter the realm of myths and legends. The first is that 20 kilos of force must be exerted on the coffee (neither one more nor one less). The second is that very strong pressure reduces the flow of water in the extraction.
If you think carefully about these statements, of which I personally was a victim for a time, you can deduce that they do not make much sense. Once the coffee has lost the air pockets inside it, it is a waste of time to try to crush it further. A light force that does not end up hurting us after hundreds of repetitions and that allows us to have more control over the level of the coffee is the best option. It cannot be established how many kilos there are, it depends on the weight and grind, but what is noticeable is the point at which the coffee has lost its sponginess and resists. That's the time to stop. As soon as the coffee comes into contact with water, this compression will be lost and little will be noticed if the pressing was 10 or 20 kilos when the pump begins to do its work.
The idea that squeezing too hard can reduce the flow of water is due to the illusory effect of having left a little more space between the coffee and the shower. This hole takes a few more moments to fill with water, which can confuse the barista and make them think that strong pressure slows down the extraction. After this small delay in the appearance of the liquid espresso through the portafilter, the flow will vary little compared to a softer compression.
We can find two types of tamper, those with a flat base and those with a slightly curved base . The latter are designed to push the coffee to the sides and better seal the space between the coffee and the cup, although it has not been proven that they reduce the tunneling effect (or chanelling ) and can generate an uneven mass with worse extractions. On the contrary, a tamper with a flat base can help us verify that the pressing has been completely leveled and leaves a more homogeneous tablet.
What is really important is their diameter and how much clearance they leave with respect to the perimeter of the bucket. The idea would be to leave no more than 0.25 mm between diameters, but here what causes problems is the cup, since not much care is taken in its manufacture and the variation in sizes can be quite large. For this reason, it is recommended to work with VST or similar precision cups whose tolerance is +/- 0.05 mm. The most recommended tampers for working with these cups are the Pullman ones, the Pergtamp by Matt Perger or the one manufactured by VST.
At the 2015 world championships we saw British barista Maxwell Colonna-Dashwood press his coffee with a strange contraption that looked like a hockey puck, the famous PUSH . Although we have not yet been able to test it because it is not yet commercialized, in theory the invention promises. The Push is a flat T-shaped disc whose depth can be adjusted for a certain weight. This way, all the coffees would have the same pressure, since the top of the tamper abuts the cup. A completely flat grind would also be achieved in each operation, which makes it ideal for cafeterias with many employees or for novice baristas.
In short, the act of pressing is much more than a simple icon of the barista world. Doing it unevenly, hitting the cup or with very wide clearances would have almost the same effect as not pressing, so to maintain consistency and obtain delicious espressos one after another, we must be aware of how we are exerting that pressure and check from time to time. when the level of it.