From wine grape residue to healthful granola bars

McKahan presents research
Gena McKahan presents her research about
granola bars made with grape-seed flour.

PULLMAN, Wash. – The remains of pressed wine grapes typically return to fields as fertilizer, but scientists are finding ways to recycle the edible remains into healthy foods.

For example, Gena McKahan’s merlot grape-seed flour granola bar is gluten free and shows an increase in antioxidant content as the amount of grape-seed flour is increased. Antioxidants found in grapes have been shown to help prevent some cancers and cardiovascular diseases.

A food science undergraduate at Washington State University, McKahan was curious about how different amounts of merlot grape-seed flour would change a granola bar’s antioxidant content when baked with other ingredients. About half the antioxidants in grapes are found in the pomace – the pulpy pile of skins, seeds and stems left over from winemaking.

McKahan made granola bars using a variety of percentages of grape-pomace flour; her data analysis showed an increase in antioxidant content as the amount of grape-seed flour increased.

“I worked in health care for seven years as an emergency room tech, so I have seen a lot of people with diabetes and celiac disease (a gluten intolerance),” McKahan said. She believes developing functional foods (foods with added nutritional value) can help an increasingly gluten-sensitive and diabetic population more easily and accessibly meet its dietary needs.

“Gluten-free products and antioxidants are also part of the health trend,” McKahan said. “The population is looking at labels.”

grape-seed flour
AprésVin flour made from merlot
grape seeds

Whether or not consumers will eat healthy snack bars depends largely on taste – an especially pertinent concern since wine flours tend to be more astringent, or bitter, McKahan said. In addition to grape-seed flour, her granola bar included buckwheat, rice, teff seed and potato starch flavor.

A consumer panel of 60 people said they preferred the granola bars containing 0 and 5 percent grape pomace flour in comparison to bars with 10 and 15 percent.

The research confirms an earlier WSU study, published in the Journal of Sensory Sciences, that suggested a granola bar with less grape-seed flour still had higher than zero antioxidant content and could be marketable. Sensory analyst Carolyn Ross and researcher Maria Rosales included sunflower seeds, another rich source of antioxidants, in that recipe.

McKahan omitted sunflower seeds in her analysis, confirming that grape-seed flour on its own provides a supply of antioxidants when baked.

Eric Leber, co-owner and president of AprèsVin (French for “after wine”) donated merlot flour for the experiments. He’s an advocate of using the whole grape. After a winemaker is done with the grapes, the seeds can be pressed for oil and then ground into flour.

Leber expressed gratitude for the partnership with WSU researchers and said those in the grape-seed flour industry can use the information to inform their customers about how to best use the flours when baking.

“Using grape pomace is all about sustainability, which is important in developing a viable wine industry from both a business and environmental standpoint,” he said. “It’s just a win-win-win.”

And with 8 million tons of grape pomace produced annually worldwide, there’s plenty of research material to go around.

Learn more about research in the WSU School of Food Science at