Choosing the right preinfusionby Simone Forgia, Claudio Santoro
The pre-infusion is a phase of coffee extraction that serves to saturate the ground coffee puck with water. This allows the extraction of all the oils and other substances during the next stage of extraction. Although the pre-infusion technique is nowadays applicable on many different types of machines, it must be said that originally it was exclusive to lever machines and subsequently an attempt was made to copy this behaviour in order to bring it to pump machines as well. Even though it has become a transversal technique applied on various types of machines, as we will see later on, it still differs in some aspects on lever-operated machines.
Like any other extraction parameter, pre-infusion should also be adapted according to the coffee used. The first parameter to take into consideration is the roast degree; in fact, lighter roasted coffees are less water-soluble and therefore water needs more time before it can penetrate inside them. If therefore a short pre-infusion is adopted on these type of roasts, the risk will be that the water will flow through the ground particles absorbing only a small part of the desired substances. The result will be an under-extracted coffee, with an unpleasant acidity, little body and probably astringent. On the contrary with the same coffee but darker roasted, a shorter or even absent pre-infusion may be necessary.
A similar reasoning can also be made about density as beans grown in altitude and therefore denser usually need more time compared to less dense ones.
A further very important factor to take into account is the dose used. As you can easily guess, the more coffee we will use, the thicker the puck will be and consequently the time needed to completely moisten it will be longer.
Finally, the last important parameter to take into consideration is the water temperature. The higher the temperature, the shorter the time needed and vice versa. This aspect can be easily understood when thinking about a cold brew. In this case, in fact, cold water is used to extract the coffee and for this very reason it takes a very long time compared to what we are usually used to, arriving even at 18 or in some cases 24 hours of extraction. Therefore, a pre-infusion at 94°C will have to be shorter than one at 90°C on the same coffee.
If you want to be meticulous, you should also adapt the type of pre-infusion to the espresso machine you have and this is where the differences in operation of each model come into play. What makes the big difference is in fact the pressure with which the boiler works and which directly affects water temperature. The popular double boiler pump machines, for example, have a dedicated boiler for steam and one for the water that is used during extraction. This means that ideally the water should have the same temperature as the grouphead and the length of the pre-infusion therefore has no influence.
On boilerless lever machines such as the Cafelat Robot, hovewer, the situation is very different because all components must be preheated as best as possible and the entire extraction phase will be a race against time before everything cools down too much.
On machines such as the La Pavoni Europiccola in contrast, the water in the boiler is at a considerably higher temperature (around 120°C) than that required to extract the coffee (90-94°C) and is cooled later thanks to the temperature difference when it comes into contact with the grouphead. If we were to analyse a graph of the temperatures during a long pre-infusion on a Cafelat Robot, we would then see that the degrees centigrade would continue to fall while on a Pavoni the opposite would happen, continuing to rise. Before applying a long pre-infusion, these aspects should also be considered.
Moving now to the available types of pre-infusion, we can identify 4 main categories and each of them leads to different results: short, long, with pressure (active) and without pressure (passive).
Usually a short pre-infusion is preferable when you want to accentuate the acidity but at the expense of body. With a long pre-infusion instead, the acidity is usually softened and the body will benefit. These types of pre-infusion are called passive because you let the water act at the operating pressure of the machine but they can become active since a slight pressure is applied with the lever. When applying this last technique, it is usually necessary to grind the coffee slightly finer but it can leave you amazed as simply adding a light pressure of 2-4 bars can considerably increase the sweetness in the cup. In order to apply this type of pre-infusion at its best it is advisable to have a pressure gauge that indicates in real time the pressure inside the grouphead; however, it can also be used on models that do not have this function. Finally, by combining an active pre-infusion with a medium-long time (15-20 seconds), it is possible to accentuate both body and sweetness.
Before concluding, however, it must be said that these are the results discovered with numerous tests on multiple coffees of various origins and roasts. However, each of them is different and not necessarily these rules are valid, but this is the beauty of our passion. The most important rule is to experiment.