What happens during grinding
Grinding breaks the bean into particles of different sizes. A finer setting makes them smaller on average and increases their accessible surface area. It also changes the resistance a coffee bed offers to water. Grind therefore affects both the extraction of compounds and the flow. How much depends on the method, grinder and recipe.
The grinder does not produce identical cubes. Small fine particles are part of the distribution. Two grinders may look as though they grind similarly yet behave differently in the filter. Terms such as sandy or caster-sugar fine help with broad orientation, but do not replace your own brewing trial.
Identify your method first
A portafilter machine normally needs much finer grounds than a French Press. With a moka pot, tamping is explicitly undesirable, and very fine espresso grounds may be unsuitable. A paper pour-over filter typically sits between these extremes. The right setting also depends on dose, bean and device.
Do not copy a number from a recipe without knowing the grinder. Setting eight on machine A may mean something entirely different from setting eight on machine B. Instead, record your own setting together with the result.
How to make sensible adjustments
- Record coffee quantity, water quantity and process. Brew a starting point and note flavour and time.
- Adjust the grinder by only one small step and according to its operating instructions.
- Allow for retained grounds. The next portion may still partly come from the old setting.
- Brew again, keeping all other quantities unchanged. Compare the cups at similar temperatures.
When finer can help
A very fast, sharp and thin extraction is a reason to try a finer grind. A blocked, harsh and dry drawdown may suggest one step coarser. Both are working hypotheses. Poorly distributed grounds, a dirty basket or unsuitable paper cannot reliably be fixed through the grinder alone.
In immersion methods, the water initially stays with the coffee. Grind size affects timing differently here than in an open filter. A longer steep does not automatically make coarse grounds equivalent to fine grounds; it is a different variable.
Compare adjacent settings
Choose two neighbouring settings and note intensity, acidity and aftertaste for each. If the difference is barely noticeable, you do not need to keep turning endlessly. First repeat one setting. Large variations between identical attempts point to an inconsistent process, not immediately to the wrong number.
The limits of accessories
A good grind matters, but cannot replace suitable beans or clean water. Even an expensive grinder cannot transform a roast whose flavour you fundamentally dislike. Start with your taste and use technology as a tool.