Roast levels: light, medium, dark

The words are not regulated and roasters do not agree with each other. "Medium" from one roaster is another roaster's "light". So the useful thing is not the label — it is knowing what physically changed inside the bean, because that is what decides how it behaves in your brewer.

Roasting drives out water and cooks sugars. A bean that has been in the drum longer is drier, lighter, more brittle and more porous. That single fact explains almost every brewing difference between a light roast and a dark one.

Light

Dense, hard, and still carrying most of what the farm put into it — the acidity, the fruit, the florals. It is also the most reluctant to give anything up, because the structure is still largely intact and water has to work to get inside it.

Practically: hotter water, finer grind, longer contact. A light roast under-extracted is sour, thin and salty-sharp, and that is the failure you will meet first, long before you manage to over-extract one.

Medium

The compromise, and the reason most people's house bag is one. Enough development to be sweet and forgiving, enough origin left to taste of somewhere. It is the roast most recipes are written against, including nearly all of mine.

Practically: whatever the recipe says. This is the baseline.

Medium-dark

Where the roast starts being the dominant flavour rather than the origin — chocolate, toast, a heavier body. Still enough structure to hold up in a pour-over. This is where most of my own numbers sit, because it is what I buy.

Dark

Brittle, porous, oily on the outside, and desperate to give everything up the moment water touches it. Origin character is mostly gone; what you taste is the roast, and there is nothing wrong with that if it is what you wanted.

Practically: cooler water, coarser grind, shorter contact. A dark roast over-extracted is bitter, ashy and hollow, and that is the failure you will meet first. All the advice for a light roast reversed, for exactly the reason you would expect.

The one thing to take away

Move the grind first, and move it alone. Temperature, time and dose all matter, but grind is the one with the most authority and the clearest signal. Change it one step, brew again, taste. If you change the grind and the temperature together and the cup improves, you have learned nothing about your coffee and will be back here next week.

What "fresh" actually means

Off-gassing is real and it is not the same across roasts. A dark roast is ready sooner and goes stale sooner. A light roast often wants a week or more before it stops tasting closed and flat. Espresso is the fussiest of all — a bag less than a week off roast will gush and channel whatever you do to the grind, and no amount of adjustment will fix a bean that is still outgassing.