What is pre-infusion?

Pre-infusion is a short phase at the start of a shot where water reaches the coffee at low pressure — often just line pressure, sometimes a gentle pump — before the machine ramps up to nine bars.

Why it helps

Dry coffee resists water unevenly. Hit a dry puck with full pressure and the water goes wherever resistance is lowest, which is how channels form in the first two seconds and stay open for the rest of the shot.

Wetting the bed gently first lets the whole puck absorb water and swell into place. When full pressure arrives, it meets a uniform, saturated bed. The practical result is fewer channelled shots and a wider margin for error in your grind.

When it matters most

• Light roasts, which are dense and resist water more.
• Fine grinds, where the pressure gradient across the puck is steepest.
• Bottomless portafilters, where you can actually see the improvement.

On a dark roast at a forgiving grind, the difference is small.

How to do it without a fancy machine

Many machines have it built in. If yours does not, you can approximate it: start the pump, stop it after two or three seconds, wait five, then resume. On a machine with a lever or a manual paddle you control it directly.

Whether this is worth doing depends on how much you enjoy the process. It is a genuine improvement and it is not the difference between good and bad coffee.

What it is not

Pre-infusion does not fix clumpy, unevenly distributed coffee. It makes an already-even bed extract more evenly. Distribution — stirring the grounds with a WDT tool before tamping — is the bigger lever, and it is cheaper.