A 2024 study found that for the most caffeine per cup, a medium roast is often your best bet — because roast level, bean porosity, and how much dissolves into the water all interact in ways that aren’t as simple as “light has more caffeine.” Here’s what the research actually showed.
The old barista debate — do dark roasts or light roasts pack more caffeine? — got a proper scientific look from a research team led by physicist Zachary Lindsey at Berry College in Georgia, with results published in the journal Scientific Reports. They set out to settle the question with data rather than lore.
What the Study Looked At
The team focused on natural and washed Ethiopian beans, testing several roast levels across brew times of one, two, and ten minutes at a 15:1 water-to-coffee ratio. To measure what was happening, they used three tools: high-performance liquid chromatography (HPLC) to quantify soluble compounds like caffeine and chlorogenic acids, scanning electron microscopy (SEM) to image the beans’ porosity and grain structure, and refractometry to gauge extraction yield. Altogether that produced a detailed picture of 30 different coffee combinations at the chemical and microscopic level.
What They Found
A few things stood out. As beans roast, their volume and porosity increase, which makes it easier for compounds to move in and out during brewing. On average, light and medium roasts measured higher caffeine than darker ones across the range — largely because some caffeine is lost the longer a bean roasts. But there’s a twist: when porosity and extraction yield were held uniform across samples, darker roasts actually held more caffeine. In other words, the outcome depends on the interplay of roast degree, bean structure, and how much you extract — not roast level alone.
The practical takeaway from the researchers: if maximum caffeine per cup is your goal, a medium roast is a smart choice. This lines up with what we cover in what roast of coffee is the strongest and the full caffeine breakdown by type.
The Bottom Line
As with most things coffee, your ideal cup comes down to personal taste. But if you’re brewing for an energy boost, a medium roast is a reliable pick — and it’s a crowd-pleasing flavor sweet spot too. Want to put the science to work? Start with fresh, roasted-to-order beans from Concord, CA and taste the difference roast level makes.
Source: study published in Scientific Reports, as reported by Popular Science.
