One of the reasons that led us to write about this subject to inaugurate the blog is the variety of tamping techniques that we have observed in different coffee shops, or among the different workers in the same premises. Also because of the different conceptions of this action when asked about it. It is one of the most iconic operations in the barista world and there are a number of reasons why good pressing is crucial.
Why should we tamp?
Once the coffee has been ground and distributed inside the cup, any air pockets that may have been trapped between the coffee particles must be removed to prevent water from passing through some areas more easily than others. This would result in an uneven extraction. In this way, the coffee is prepared so that the discharge and passing of water is homogeneous throughout the product. This is the only way to have a uniform extraction espresso after espresso, and to minimise the channeling effect for sweeter drinks.
With experience and tactile memory, we will also end up knowing if the grinding point we have obtained is the right one and if the distribution of the coffee in the cup is uniform.
A good tamping
Knowing that the aim of pressing our coffee is to achieve a homogeneous extraction, it is easy to understand that the best tamping is that which is completely leveled. Tapping with the tamper on the sides should be avoided, as this can open cracks in the perimeter that are difficult to seal with a second pressing.
A good technique that I personally find effective is to place my index finger and thumb on the edges of the tamper, while using the rest of the palm of my hand to push the tamper downwards. This way I control that both fingers go in at the same time and the tamper is leveled. 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 pulling the tamper out of the bucket, it is important not to hit the sides and to do it gently so that, in case of a small tamper/bucket clearance, cracks do not form due to suction. Turning the tamper at the end is a flourish that can be avoided.
How much force should we apply?
We enter into the realm of myths and legends. The first is that 20 kilos of force must be exerted on the coffee (no more and no less). The second is that too much pressure reduces the flow of water in the extraction.
If you think carefully about these statements, to which I personally fell victim for a while, 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 is not possible to establish how many kilos it is. It depends on the weight and the grind, but what is noticeable is the point at which the coffee has lost its fluffiness and puts up resistance. This is the moment to stop. As soon as the coffee comes into contact with water, this compression will be lost and you will hardly notice whether the pressing was 10 or 20 kilos when the pump starts to do its job.
The idea that pressing too hard can reduce the water flow is due to the illusory effect of having left a little more space between the coffee and the shower. This gap takes a few moments longer to fill with water, which can confuse the barista into thinking 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 from a softer compression.
Tampers.
There are 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 seal better the space between the coffee and the coffee cup, although it has not been proven that they reduce the tunnel effect (or chanelling) and can generate an uneven mass with worse extractions. On the other hand, a tamper with a flat base can help us to check that the pressing has been completely levelled and leaves a more homogeneous pod.
What is really important is the diameter of the tamper and how much clearance it leaves with respect to the perimeter of the ladle. The idea would be to leave no more than 0.25 mm between diameters, but here the problem lies with the barrel, as it is not so carefully manufactured and the size variation can be quite large. For this reason, it is recommended to work with VST or similar precision ladles with a tolerance of +/- 0.05 mm. The most recommended tamper to work with are the Pullman, Matt Perger’s Pergtamp or the one made by VST.
At the 2015 world championship 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 try it out because it is not yet commercially available, in theory the invention is promising. The Push is a flat T-shaped puck that can be adjusted in depth for a certain grammage. In this way, all coffees would have the same pressure, as the upper part of the tamper would stop against the spout. A completely flat grind would also be achieved in each operation, which makes it ideal for coffee shops with many employees or for novice baristas.
In short, pressing is much more than just an icon of the barista world. Pressing unevenly, banging the cup or with very wide gaps would have almost the same effect as not pressing, so to maintain consistency and obtain delicious espressos one after the other, you have to be aware of how you are pressing and check the level of pressure from time to time.
Pablo Caballero
