One study found that dark-roasted coffees are easier on the stomach than light or mild roasts because they contain a particular ingredient that keeps your stomach from producing too much acid.
For the study, researchers took human cells that regulate acid secretion in the stomach and exposed them to different types of coffee: regular, dark-roast, mild, decaffeinated, and low-acid. They found that different compounds in the different roasts had compounds that do indeed cause stomach cells to produce more acid. The main culprits were caffeine and two different plant compounds, catechols and N-alkanoly-5-hydroxytryptamides. But they also found that another compound, N-methylpyridinium (NMP), had the opposite effect. NMP was generated as the coffee beans were roasted, and the longer they roasted, the higher the levels of NMP that were present.
Dark-roasted coffee can contain as much as twice the levels of the stomach-friendly compound NMP as light-roasted coffees, though that can vary depending on the variety of the bean. Their research also found that coffees being marketed as low-acid or easy on the stomach should work because they lower levels of acid-producing compounds, but you may not want to drink them for other reasons. Manufacturers of those coffees usually treat raw coffee beans with steam or other chemical solvents, such as ethyl acetate and dichloromethane, prior to roasting. (Check out what happened when one writer swapped her morning coffee for matcha tea.)
So, if you want to enjoy coffee but don’t want to expose yourself to chemical solvents, the easiest thing to do is try dark-roasted coffees first. But which one should you buy? Here are a few tips on reading labels.
Look for geographic names
Some coffee companies are explicit and label coffees as “medium roast” or “dark roast.” Others, however, use coffee terminology to describe their roasts, and more often than not the names are geographic.