What does dialling in mean in coffee?

Dialling in is the process of adjusting brewing variables - grind size, dose, water temperature, and brew time - to find the optimal extraction parameters for a specific coffee. The term is used most commonly in espresso, where small changes in grind size produce significant changes in extraction speed and cup character, but the concept applies across all brew methods.

For home roasters, dialling in is an inherent part of working with every new batch. Because roast level, bean density, and freshness all affect how a coffee extracts, a profile that works for one roast may need adjustment for the next. A lighter roast typically requires a finer grind and higher water temperature than a darker roast from the same beans; a very fresh roast may need a slightly coarser grind than the same coffee after a week of rest.

The practical process: start with a reference recipe, brew a cup, evaluate it - is it too sour (underextracted - grind finer or brew longer), too bitter (overextracted - grind coarser or reduce brew time), or balanced? Adjust one variable at a time, taste again, repeat until the cup expresses what the coffee has to offer. It's iterative work, but it's how you learn what a coffee is actually capable of.