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Ever get a sour stomach after your morning coffee? Well, you might end up switching to a dark roast—because that coffee concoction¹ may leave you with a happier tummy. That's according to the research presented at the American Chemical Society meeting in San Francisco.

Some coffees are labeled "stomach friendly," because they're steam treated to drive out caffeine and other chemicals thought to cause gastrointestinal distress². But food chemists wanted to know exactly which chemicals were behind the heartburn. So they took extracts of two coffee blends—one light, one dark—and their steam-treated counterparts. Each extract proved to be a unique chemical mix, with different amounts of caffeine and other compounds.

When the researchers served these coffee extracts to cultured human stomach cells, the cells jacked up acid production. Except in the case of one extract, high in a compound called N-methylpyridinium—a chemical produced in the roasting process that's not found in raw green coffee beans. And the darker the roast, the more there is. Now the researchers are test roasting a stomach-soothing N-methylpyridinium blend. Human trials will determine if it has all the boldness with none of the reflux.