Espresso Preinfusion

Espresso Preinfusion

Espresso brewing is sometimes considered an art, with countless variables to be fiddled with, different techniques, and a huge number of different results you can get from the same coffee. 

Traditionally, espresso is brewed at 9 bars of pressure, maintained throughout the brew. That is, once you’ve loaded the portafilter into the machine and hit go, the pump kicks on and slams the coffee at full power for the entire extraction. 

This makes the brew consistent: the same pressure is maintained on the coffee for the whole process. Consistency is one of the key indicators of a good extraction, as it means that all of the coffee is taking part in the whole brew, and generally results in a balanced and well extracted cup.

However, consistent pressure isn’t the only factor in consistency. 9 bars of pressure is a huge amount of force – 9 times the pressure of our atmosphere – and this violent jet of water can cause its own problems. If the puck of coffee wasn’t prepared properly, there might be air pockets, cracks, or different densities hidden in the bed of coffee. These weak points will let the high-pressure water spurt straight through, causing what’s called a channel. Water flowing through a channel isn't coming into contact with all the coffee, and will lead to uneven extraction, despite the even pressure.

One solution that baristas have been using as machines have enabled ever-more granular control over extraction and brewing profiles is called preinfusion. Here, the brew starts with a lower pressure, which is slowly ramped up over the course of the extraction until the full 9 bars of pressure is reached. 

This gentle start helps to get all the coffee evenly saturated before cranking up the pressure. That way, water slowly soaks into the coffee, removing inconsistencies from the puck and creating a homogenous, well-soaked bed of coffee that water then passes through evenly. 

This does require some fancy tools to achieve. Some machines have a paddle or lever which allows the barista to manually control the pressure in the grouphead over the course of the brew. Set-ups geared toward high-volume environments where fiddling with each shot is too time consuming might have electronically programmed preinfusion profiles where the machine handles the pressures automatically. Or, if you’ve only got an on/off button, you can achieve a kind of preinfusion by simply shutting the pump off for a moment after the first few seconds of extraction. 

A well executed preinfusion can help to improve the evenness of an espresso, which will not only achieve a more balanced tasting coffee, but also allow a higher extraction overall. This lets us extract more flavour from the coffee, bringing out more of its natural characteristics, without it becoming over-extracted or unbalanced. 

Want to dig below the surface of espresso brewing? We offer barista courses for pros and home baristas alike, where you can go alllllll the way down the rabbit whole of espresso. Check it out here.