Puck prep and channeling

The puck is the whole game

The puck is the bed of coffee in the basket, and the pump pushes water through it at full pressure. Water is lazy: it takes the easiest route.

Every route equally hard

If the bed is even, water soaks through everywhere at the same pace. A loose patch, a clump or an air pocket, and the water rushes through there instead. Puck prep is simply making every route equally hard.

Channeling tastes like both

When water finds a shortcut, that’s channeling. The coffee along it gets far too much water and turns bitter and drying; the rest barely gets any and stays sour. The cup is both at once, and the shot often runs fast.

A bottomless portafilter has no spouts, so channeling shows as spurts and sprays, like an aggrieved hose. The spent puck tells you less: a wet, soupy one can follow a lovely shot.

Where is the water getting through fastest? loose

• The loose patch: The channel. Water under pressure takes the easiest route, and this one is wide open.
• The tamped bed: Evenly packed, so the water has to work — which is why it went looking elsewhere.
• The basket floor: The basket below the bed. Not the bottleneck: the coffee above it is what slows the water.

A shot that channels usually runs…

Answer: Faster than usual. Faster. The water has found a shortcut, so less of the bed slows it down — and the cup comes out sour and bitter at once.

Break up the clumps

Grind into the basket, then break up the clumps. WDT — stirring the grounds with a few very thin needles — was shared on a home-espresso forum in 2005 for exactly this. Tap the basket gently to settle it.

Put the prep in order.

1. Grind into the basket
2. Stir out the clumps
3. Tap the basket level
4. Tamp straight down

Grind, stir, tap, tamp. Every step aims at the same thing: no loose patch and no clump for the water to find.

Level beats force

Then tamp: press straight down, firm and level. Level matters far more than force; save that for jar lids. Tests found a harder tamp changes very little; a tilted one leaves a thin side for the water to find.

Some machines start with pre-infusion: a gentle, low-pressure soak so the whole puck is wet before full pressure arrives. Some people mist the beans before grinding, to tame static and clumps.

Pre-infusion and a misted bean are best thought of as…

Answer: Small helpers, once the basics are right. Small helpers. Each can help a little; none of them rescues stale beans or a wrong grind, so sort those out first.