Reference · choosing coffee

Choosing beans and roast levels

A coffee bag usually tells you three things worth reading: the species (arabica, robusta or a blend), the roast level, and a roast date. Here is what each means for the cup, and how to keep beans tasting good once they’re home.

What roasting does

Green coffee beans already contain the acids, proteins, sugars and caffeine of roasted coffee, but none of the roasted taste. Heat creates it: the Maillard reaction and other reactions build flavor, sugars caramelize into caramel notes, and unpleasant-tasting chlorogenic acids are broken down. Partway through, at about 175 °C (347 °F), roasting switches from absorbing heat to releasing it. Two audible milestones mark the progress:

• First crack at about 196 °C (385 °F): beans crack and expand. Light roasts begin here.
• Second crack at about 224 °C (435 °F): beans turn brittle and oils come to the surface.

Along the way beans lose 15–18% of their mass, mostly water, while their volume roughly doubles.

Roast levels at a glance

Temperatures and descriptions from Wikipedia’s coffee-roasting table. Roasters use these names loosely, so treat them as a guide.

How to pick a roast

• If you like bright, fruity or tea-like coffee, or want to taste where a coffee came from, choose light.
• If you want a balanced everyday cup, medium keeps some origin character with more body.
• If you drink coffee with milk or like bold, roasty flavors, dark roast stands up to it.

Does dark roast have more caffeine?

No. Caffeine is stable up to about 200 °C and only decomposes around 285 °C, a temperature roasting rarely reaches, so roast level doesn’t change caffeine content much. Because darker beans are less dense, a scoop of light roast actually contains slightly more caffeine than the same scoop of dark roast. Measuring by weight removes the difference. More on that on our caffeine facts page.

Arabica vs. robusta

Vietnam, which grows mostly robusta, is the largest robusta exporter. Most robusta goes into instant coffee, and it is often used as a filler in lower-grade blends — so if a label doesn’t name the species, check the blend description.

Keeping beans fresh

Freshly roasted beans release carbon dioxide — up to about 10 liters per kilogram for dark roasts. That gas actually protects them from oxidation, which is why coffee bags often have a one-way valve that lets gas out without letting air in, and why a few days of resting (degassing) after roasting is reported to give the best results. After that, the enemies are air and light.

The simplest rule of all: buy whole beans in amounts you’ll use within a couple of weeks, and grind right before brewing, as the National Coffee Association recommends. Then follow our brewing basics.