Dark roast coffee

A dark roast is defined by how far the beans went, not by what they taste of. Somewhere in and after second crack the sugars stop caramelising and start burning, the acids that carried the origin flavours break down, and what is left is the roast itself: bittersweet, low in acidity, heavy in the mouth. That is the whole trade. You lose the farm and you gain consistency.

Second crack is the line, and it is audible

Roasting coffee produces two audible events. First crack, at roughly 196C, is moisture leaving the bean and it sounds like popcorn. Second crack, some thirty degrees later, is the cell walls themselves fracturing and it sounds like breaking twigs. A medium roasted coffee is pulled well before second crack. A dark roast is pulled during it or after it, and every difference on this page follows from those last thirty seconds. What a roaster actually does covers the rest of the curve.

It is not stronger, and it holds slightly less caffeine

Dark roast tastes bolder because bitterness reads as strength, but strength in a cup is a ratio of coffee to water and that is set by your recipe rather than by the roaster. Caffeine is barely touched by roasting at all. What changes is density: a dark roasted bean has lost more water and more mass, so a scoop of it holds fewer beans and marginally less caffeine than the same scoop of a light roast. Weigh instead of scooping and the difference all but disappears. How much caffeine a cup of coffee holds has the numbers.

French, Italian and Vienna are styles inside the band, not levels above it

No industry body defines them. One roaster's French is another's Italian, which is why the Specialty Coffee Association measures roast as a colour reading rather than by name. Loosely: Vienna sits at the start of second crack, French in the middle of it, Italian at the far end where the bean is nearly black. A coffee is not French roast or dark roast, it is a dark roast in the French style, and we file by what the roaster states rather than by the label on the front. What Vienna roast is goes further.

The oil on the beans is a clock

Dark roasted beans push oil to the surface, and that oil is exposed to air from the moment it appears. It is not a fault and it is not a mark of quality either; it is a sign the roast went far enough to break the cell structure open. It does mean dark roasts stale faster than lighter ones, and that they will eventually leave residue on a grinder's burrs and a hopper's walls. Buy smaller bags more often, keep them sealed and out of the light, and prefer a roast date to a best-before. Coffees that print a roast date are listed on their own page, and are oily beans bad answers it directly.

Brew it where bitterness is an asset

Dark roasts are forgiving under pressure and in immersion, and unforgiving in filter. Espresso, moka pot and French press all suit them: the short contact time or the pressure keeps the bitterness in proportion, and milk has something to push against. Pour over is where a dark roast is most likely to go wrong, because a long contact time keeps pulling from beans that have little left to give beyond ash. If you are brewing filter, drop the water a few degrees below boiling and grind a notch coarser than you would for a medium. Water temperature and grind size both matter more here than anywhere else on the scale.

Who it is for

Somebody who takes coffee with milk, who wants the same cup every morning, or who grew up on the taste of a supermarket dark roast and likes it. That last one is not a small reason. It is also the right band if your brewer is a moka pot or an inexpensive drip machine, both of which flatter a roast that can afford to lose a little.

Who it is not for

Anyone chasing the fruit and florals a single origin is bought for. Roasting hard is how a roaster makes different beans taste alike, so a dark roast on a rare lot is money spent on something you will not taste. If the words on the bag that appeal to you are berry, citrus or floral, you are at the wrong end of the scale. What survives down here is chocolate, earthy and woody and smoky.