How the Gauge Shows Pre-Infusion

On some machines the needle doesn't leap up when the shot starts. It stays low, then climbs. That's pre-infusion, and the gauge is showing you the machine doing it on purpose.

What pre-infusion is

Pre-infusion means wetting the coffee gently before full pressure arrives. One maker's manual describes it this way: the low pressure pre-infusion gradually increases water pressure to gently expand the grinds for an even extraction, before increasing to full pressure¹.

So there are two stages in one shot. First comes a soft, low-pressure stage. Then the machine moves up to its working pressure.

Not every machine has this. It depends on the design, so whether yours does is a question for your manual.

What the needle does

The same manual says the needle will sit in the pre-infusion zone at the start of the extraction. That shows the machine is in low pressure pre-infusion mode¹. A second copy of the manual's gauge page describes a low pressure pre-infusion zone at the start that indicates low pressure mode².

Read that carefully. The zone on the dial isn't a place to aim for. It's a label for a stage. The needle is meant to be there at the start, and to move on.

Who controls the length

On that maker's machine, the length of this stage can be under the user's control. A press-and-hold on the shot button keeps the machine in low pressure pre-infusion until the button is released, and extraction then carries on at full pressure¹.

That means a slow rise on the gauge can be your own choice, not a fault. How yours works, and whether it has any such control, is in your manual.

Slow rise or slow pump?

A slow start isn't automatically pre-infusion, and a slow start isn't automatically a problem. If your machine isn't built with a pre-infusion stage, a needle that crawls at the start could be something else, and the manual or maker is the place to ask.

Two things help you tell them apart:

• Does the slow climb happen every shot, in the same way, from the first second?
• Does your manual describe a low-pressure start or a pre-infusion zone for your model?

If both answers are yes, you're likely watching pre-infusion. If the answer to the second is no, or the pattern changes from shot to shot, contact the maker. Don't open the machine to look.

Judging the shot

A glossary calls the middle of the shot the reading that matters most for brew pressure³. So after pre-infusion has finished and the needle has settled, that's the moment to read. The mid-shot notes describe it, and the dial-reading page explains units and bands.