The myth
Dark roast tastes stronger, so most people guess it has more caffeine. It's one of the most common coffee myths. Caffeine hardly changes in the roaster: what changes is the flavour.
So if you want more caffeine, a darker roast won't give it to you. A bigger cup, more coffee per cup, or a different bean will (see arabica vs robusta).
What roasting does
Raw coffee is a pale green seed: hard, and it smells of grass, not coffee. Every flavour you love is made in the roaster.
Over about 10 to 15 minutes the beans brown, and that browning builds hundreds of aromas. Along the way they pass two landmarks:
- First crack, at about 196°C. The beans pop like popcorn as steam escapes. Light roasts stop soon after this.
- Second crack, at about 224°C. Dark roast territory. Oils sweat out to the surface, which is why dark beans look shiny and oily.
Those temperatures are bean temperatures and vary by roaster, so take them as "about". On the way, the beans swell up and lose about 15 to 20% of their weight, mostly water.
How the roasts taste
| Light roast | Dark roast | |
|---|---|---|
| Roasted to | Just after first crack | Second crack |
| Looks | Light brown, dry, matt | Almost black, shiny, oily |
| Tastes of | The bean: fruity, floral, bright acidity | The roast: bitter-sweet, smoky, dark chocolate |
| You taste | The farm | The roast |
| Caffeine | About the same | About the same |
Light roasts keep the bean's own flavours, so a light-roasted single-origin coffee lets you taste where it's from. In a dark roast those origin flavours fade and the roast takes over.
Why "by the scoop" changes the answer slightly
Per bean, the caffeine is about the same. But dark beans are bigger and lighter after the longer roast, so a scoop holds a little less coffee by weight, and slightly less caffeine. A scoop of smaller, denser light beans holds a touch more. Weigh the coffee instead and it flips: gram for gram, dark roast has slightly more, because it lost more water in the roaster. Either way, the difference depends on the beans and is too small to notice in the cup.
Is your coffee fresh? Read the bag
Roasted beans are at their best for a few weeks. Two things on the bag tell you about freshness:
- The roasted-on date. Use the beans within about a month of it.
- The one-way valve, the little round vent on the front. Fresh beans give off CO2 for days after roasting, and the valve lets it out while keeping air out. It shows the beans were packed while still giving off gas; check it together with the date, not instead of it.
What doesn't help: the best-before date. It is often a year after roasting. The coffee is safe to drink by then, but long past its best. And the roast level on the bag tells you the flavour, not the freshness.
Common mistakes
- Buying dark roast for the caffeine. It tastes bolder, but the caffeine is about the same.
- Going by the best-before date. Look for the roasted-on date instead.
- Thinking shiny beans are glazed or roasted in oil. The shine is the bean's own oil, pushed out by the longer roast.
Questions people ask
Does dark roast have more caffeine?
No. Roasting barely changes the caffeine. By the scoop, dark roast has slightly less; by weight, slightly more; but the difference is too small to feel. It just tastes bolder.
What is first crack in coffee roasting?
The moment, at about 196°C, when the beans pop like popcorn as steam escapes. Light roasts stop soon after it.
Why are dark roast beans oily?
The longer roast pushes the beans' own oils to the surface, which makes them look shiny.
How long do coffee beans stay fresh?
They're at their best for a few weeks after roasting. Use them within about a month of the roasted-on date.
