The short version
- Weigh the dose and the output. Everything else is guessing.
- Give the machine a full warm-up before the first shot that counts.
- Distribute the grounds before tamping — most channelling starts there.
The most common message we get about espresso is some version of “my shots are sour and I think I need a better machine”. Usually the machine is fine.
Weigh both ends
A scale that reads to 0.1 g is the single highest-return purchase in home espresso, and it costs about $25. Weigh the dry coffee going in and the liquid coming out. Until you do that, every adjustment you make is being measured against a number you do not know.
Start at 18 g in, 36 g out, in about 28 seconds. That is not a rule, it is a starting point you can move away from deliberately.
Wait for the machine
Every machine we have measured takes at least twelve minutes from cold to a stable brew temperature, and several take twenty. The first shot pulled at minute five will taste different from every shot after it.
Distribute before you tamp
Most channelling — water finding a path through the puck and running out early — starts as an uneven bed of grounds, not as an uneven tamp. Stir the grounds in the basket with a thin tool before tamping. It takes four seconds.
Change one thing at a time
Grind, dose, and time all interact. Change one, pull two shots, taste. Change two at once and you have learned nothing.
