What Is Pre-Infusion in Espresso?

Pre-infusion is the soft start of an espresso shot. Water reaches the coffee gently first. Full pressure comes after.

The plain definition

Espresso is¹ "a concentrated form of coffee produced by forcing hot water under high pressure through finely ground coffee beans". That pressure is the main event. Pre-infusion is what some machines do just before it.

La Marzocco makes home machines. Its definition: water flows in continuously at low pressure and saturates the puck. A higher, steady pump pressure then takes over and the brew begins.² The puck is the compact disc of ground coffee sitting in the basket.

So there are two ideas in one sentence. The water is low pressure at first. And the aim is to wet the whole puck before the push.

What the makers say it's for

The Lucca Tempo manual calls it several seconds of gentle saturation of water to the coffee puck before full nine-bar pressure is applied during extraction.³ "Bar" is a unit of pressure, and the manual names nine of them for the main brew.

That's the stated purpose in both sources: saturate the puck gently first. This site sticks to what makers write. It doesn't promise a better taste, because the pages saved here don't make a promise you could count on.

Why you can't see it

Look at the spout during the soft start and you'll usually see nothing yet. La Marzocco notes that pre-brew and pre-infusion happen before visible extraction.² The work is going on inside the group head, the part that holds the portafilter, and the cup stays empty.

That's why the feature is easy to miss. You read it from the clock, a gauge or a display, not from the coffee.

Where the names get muddled

Makers use a few words for a soft start. "Pre-infusion" and "pre-brew" are not quite the same thing in La Marzocco's wording. Pre-brew is an on, off, on pattern that wets the top of the puck.² Pre-infusion is one continuous low-pressure flow. Other makers may use the words differently, so read the description in your own manual instead of trusting the label.

Pre-infusion also gets confused with the bloom in pour-over coffee. They aren't the same thing, and the next page sorts that out.

How machines get there

Different machines make the soft start in different ways. A pump machine can run its pump for a short time and then pause, or let water in at the water line's own pressure. On La Marzocco's Leva-X lever machine, the maker says holding the lever position controls it. Those routes have their own pages: pump machines and lever machines.

If your machine has a setting for it, the numbers you can change are in the maker's manual. What the manuals say about time and pressure shows a few examples.