SAN FRANCISCO, March 21, 2010 - With stomach irritation preventing almost 2 out of every 10 people from enjoying coffee, scientists today reported discovery of several substances that may be among the culprits responsible for brewing up heartburn and stomach pain in every cup.

Their report, presented here at the 239th National Meeting of the American Chemical Society, included the counter-intuitive finding that espresso, French roast, and other dark-roasted coffee may be easier on the tummy because these roasts contain a substance that tells the stomach to reduce production of acid.

The research could lead to a new generation of stomach-friendly brews with the rich taste and aroma of regular coffee, the scientists said.

The processes used to produce stomach-friendly coffee also can reduce the amount of healthful substances in the coffee, including some that scientists have linked to benefits such as protection against diabetes and heart disease, say Veronika Somoza, Ph.D. from the University of Vienna in Austria. In addition, the processing can affect the robust taste and smell of coffee.

In their research, it was found that caffeine, catechols and N-alkanoly-5-hydroxytryptamides are the components which stimulate molecular mechanisms of stomach acid secretion in human stomach cells. Most of them are indeed removed by steam or solvent treatment of the raw coffee bean. It was found that there's no single, key irritant. However, a mixture of compounds seem to cause the irritant effect of coffee.

The scientists unexpectedly found that one of the coffee components, N-methylpyridium (NMP), seems to block the ability of the stomach cells to produce hydrochloric acid and could provide a way to reduce or avoid stomach irritation. Since NMP is generated only upon roasting and not found in raw coffee beans, darker-roasted coffees contain higher amounts of this stomach-friendly coffee ingredient.

The scientists are testing different varieties of raw coffee beans and different roasting methods in an effort to boost NMP levels to make a better stomach-friendly coffee. They hope to test the new brew in human volunteers later in 2010.