Before we slam coffee grounds with ~9 atmospheres of water pressure, it’s polite to give them a warning. This preparatory step before pressurisation is often called “pre-infusion”, and it is a crucial step for making delicious espresso.
Wetting the coffee and letting it soak in has two main effects on the resulting extraction. Firstly, it swells the puck; reducing the chances of an easy way through for the high pressure water. Secondly, it lets this brewing water pass through more easily, allowing us to use a finer grind size. This means there's a more even extraction, with more coffee surface area to pick up deliciousness. Both big wins in the espresso play book!
Some Baristas choose to pre-infuse quickly by saturating the puck at full pressure and then pausing for a set number of seconds. Others will choose to add water at a lower pressure for a longer time and increase pressure once drips appear from beneath the basket. There has been some advancements in our understanding of pre-infusion with more advanced espresso machines but there’s still a long way to go. One thing’s for sure, it’s not simple.
Once you’ve settled on a pre-infusion style, the only problem is that it’s very finicky. A second too long when adding the initial water and you’ll speed the shot up considerably. A second too short and you’ll leave half the coffee bed dry leading to an uneven extraction. Espresso machines with paddles for manual pre-infusion are notoriously difficult to wrangle like this in a medium or high volume environment. They require a lot of attention and slow down the rest of the bar just to get it right. This is one the many aspects of coffee preparation where doing things even slightly differently each time is anathema to consistency.
With such a small margin for error, it’s obvious that the solution is once again “let a machine do it”. Many manual machines already automate this feature, and of course all fully automatic machines do as well. When a repetitive job requires full human focus and energy just to get something right, it always pays off to look at other options. Barista technique should be so much more than just waiting for some drips to come out of an espresso basket so you can swing a paddle to flip a switch at the right moment!