Dialling in a new bag

Fix everything except the grind

Dialling in fails when two things move at once. Before the first shot, fix these and leave them alone:

• Dose: whatever your basket is made for, weighed. An 18 g basket gets 18 g, every time, to the tenth of a gram.
• Ratio: start at 1:2. An 18 g dose gives 36 g in the cup, weighed, not guessed by eye.
• Water temperature: whatever your machine does. Do not touch it yet.
• Puck prep: the same routine every shot, or you are measuring your technique rather than the coffee.

Now the only thing you change is the grind, and the only thing you read is the time.

The target

18 g in, 36 g out, in 25 to 30 seconds from the moment the pump starts.

That window is a starting point, not a law. It exists because it lands most medium roasted coffees in a reasonable extraction range, which makes it a sensible place to begin before you deliberately leave it.

The loop

1. Pull a shot to the target weight and note the time.
2. Faster than 25 seconds: grind finer.
3. Slower than 30 seconds: grind coarser.
4. Make the first correction big enough to see. Half of what you think, and you will spend six shots creeping towards an answer.
5. Purge a couple of grams after each adjustment, or you are brewing the old setting.

Once the time lands in the window, taste it. The clock got you into the range; your palate decides the rest.

Reading the cup

Tastes	Meaning	Do
Sour, sharp, thin, salty	Under extracted	Grind finer, or raise temperature
Bitter, drying, ashy	Over extracted	Grind coarser, or lower temperature
Sour and bitter at once	Channelling	Fix the puck prep, not the grinder
Correct but hollow	Ratio	Try 1:2.2 or 1:2.5

That third row is the one people miss. Sour and bitter together is not a grind problem, and grinding either way will make one of the two worse.

Roast level changes the starting point

A light roast is denser and less soluble, so it usually wants a finer grind, a longer ratio towards 1:2.5, and a higher temperature. A dark roast is porous and extracts easily, so it wants a coarser grind, a shorter ratio, and a lower temperature before it turns bitter.

When to stop

Stop when two consecutive shots taste the same and you like them. Write down the grinder setting, the dose, the yield and the time on the bag itself.

Then expect it to drift. A bag roasted four days ago is still releasing carbon dioxide, which resists the water and makes the shot run fast, so you will grind finer across the first week and then hold steady. That drift is the coffee changing, not your technique failing. Resting coffee after roasting explains where that gas goes and how long to wait for it.