@coffeegeek @coffee so just to clarify, dark roast has more caffeine by weight, but because it "puffs" more it takes up more volume and thus you end up with less caffeine in the brewed cup?

Is that where the idea of "light roast has more caffeine than dark roast" comes from, that you get more light roast coffee in each volume-measured serving?

@truth_hound @coffee

To be clear: dark roasted coffee has bigger beans because gas expansion during roasting makes them bigger.

If you take a 2 cup pyrex measuing cup, and pour in a french roast to the 16 fluid ounce, 2 cup marker, and then do the same with a light roast, the french roast may weigh 400g, and the light roast will be around 450g or more.

Take both coffees, measure out 20g to grind and brew with. Visually, the french roast's dose will LOOK bigger, but be the same weight. It will also have a higher percentage of caffeine because it retained the caffeine while losing other elements in the roast, when you brew.

HOWEVER... if you use a tablespoon scoop to measure, and measure out, VISUALLY, a tablespoon of dark roast, and a tablespoon of a light roast, and brew with those volumes, the caffeine levels would be closer to equal in the cup, and it's possible the LIGHT roast might have more caffeine in the cup.

But that's because you used less actual coffee (by weight) to brew the dark roast coffee than the light roast coffee. ;)