The pre-infusion system is an increasingly popular process in espresso machines. What is pre-infusion? Basically, it consists of applying hot water to the ground coffee for a few seconds at a much lower pressure than that used to extract the espresso. After the pre-infusion, the coffee will be slightly moistened and will have increased in size a little.
Pre-infusion is only an aid to achieving a perfect espresso extraction. And it is of little or no use if the entire pre-infusion process (grinding, pressing) has been done correctly.
For this last reason, many professional baristas debate whether or not to pre-infuse before extracting the espressos. In the domestic sphere, we dare to say that pre-infusion is very useful in almost all situations. It is not in vain that most professional coffee machines or hotels do not have this option (we can make a pre-infusion, but manually). And yet, most modern espresso machines have integrated pre-infusion functions.
What is the pre-infusion for?
Basically, to achieve two goals: firstly, thanks to pre-infusion, the ground coffee in the filter gets wet or soaked for a short time. It is enough to homogenize the coffee and avoid differences in pressure, volume or small air chambers that could affect the final result. It is, to be understood, a way of concealing small defects or irregularities in the coffee bed.
The second great objective of making a pre-infusion is that the ground coffee filter will then offer much greater resistance to the passage of water at full pressure (around 9 bars, if everything is correct). This higher water resistance is supposed to result in better extraction of the aromas, flavours and nuances of the roasted coffee. In theory, the higher pressure resistance also helps the coffee to come out with more cream.
How is Preinfusion done?
There are several ways to make a pre-infusion on our ground coffee.
Some coffee machines allow manual pre-infusion (by briefly opening the water tap, closing it after a few seconds and then activating the normal espresso extraction). We should also stress that, although in recent times, pre-infusion systems have been associated mainly with espresso machines, pre-infusion is a process that can be practised in any coffee machine.
We continue with more cases: automatic coffee machines, for example, usually pre-infuse automatically because they need the filter not to be obstructed, and also usually grind slightly coarser than if a separate grinder, specifically for espresso, is used. The Miele CM 6310 is a good example of this segment.
Other manual espresso machines (such as the Rancilio Silvia, the Graef ES 85 or the Severin KA 5991) have an option that enables or disables pre-infusion. Others go further and allow you to manipulate and alter various variables to play with various types of pre-infusion.
In this image, you can see the effects of pre-infusion on the same coffee bed. On the left is a short pre-infusion (2 seconds), and on the right, a slightly longer pre-infusion (4 seconds).
Is pre-infusion necessary?
No, not at all. We have already seen that a pre-infusion system aims to extract more aromas and nuances from the ground beans. Coffee makers have not used pre-infusion systems for many years, and nothing has ever happened; their coffee has remained excellent.
Pre-infusion should be seen as an extra or additional method to achieve more intense flavours. Also, as an aid: it is a process that can help us when there are problems with holes, density differences, or air chambers in the ground coffee bed, and that does no harm and has no effect in other cases.
But we can never consider pre-infusion as the standard way of preparing coffee, nor as a quality that causes great differences, as many brands and many models of coffee machines advertise. In fact, as we said at the beginning if the thickness of the grinding and pressing is perfect and close to perfection, the pre-infusion process will be useless.
Useful yes, necessary never.
How long does the pre-infusion last?
This is an impossible question to answer. Don’t make the mistake of relying on testimonials you read from other users because the ideal pre-infusion time will be determined by a multitude of factors. The pre-infusion time depends, for example, on the type of coffee used, the temperature or the weight of the dose.
The best advice we can give you is to clearly establish your dose and your ideal temperature for making espresso. When you are clear about these two factors, then it’s time to experiment.
Make different extractions with various pre-infusion times (no less than 2 seconds and no more than 8-10 seconds), taste the resulting coffees, take your notes, and be patient to draw conclusions.