Sour or bitter?

Extraction is the process in which water draws flavours out of ground coffee. They do not all come out at the same speed. Acids go first, then sweetness, and bitterness last. That is why the taste of a shot is really a report on how long and how easily the water worked.

Sour, sharp, empty

The water went through too fast or too cool and drew out only the acids. That is under-extraction. The shot usually runs fast and seems thin.

• Grind finer (the most important one).
• Lengthen the ratio, for example from 1:2 to 1:2.3.
• Check that the machine is warmed up, and raise the temperature if you can set it.

Bitter, astringent, dry at the finish

The water worked too long or too hot and drew out what you did not want as well. That is over-extraction. The shot usually runs slowly and leaves a dryness on the tongue.

• Grind coarser.
• Shorten the ratio, for example from 1:2 to 1:1.8.
• Lower the temperature if you can set it. Dark roasts like it lower.

Sour and bitter at the same time

That is not a contradiction, it points to channelling. The water finds an easier path through part of the puck, so part of the coffee is over-extracted and part under-extracted.

A bottomless portafilter helps you see it, because you watch the extraction from below. The fix is most often in puck preparation: WDT down to the bottom, a level tamp, and the portafilter resting flat on the mat. A puck screen can help the water spread more evenly. If it keeps happening, try a slightly coarser grind too, because grinding too fine also causes uneven flow.

Watery, no body

Too little coffee for the ratio you are aiming for. Raise the dose by a gram or shorten the ratio. Look at the roast date as well: there is no single rule for all coffees, but coffee usually needs a short rest after roasting, and dark roasts age faster than light ones.