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Grape pomace, also known as marc, is the leftover material after grapes are pressed during winemaking. Some wineries repurpose it as compost for fertilization, while others sell it to biogas companies for renewable energy generation. Mint/Getty ImagesKey Insights
- Winemakers creatively reuse grape pomace (or marc), the leftover substance from winemaking, in eco-friendly ways such as using it as fertilizer, animal feed, and even supplying it to biogas companies for renewable energy production.
- Rich in antioxidants, fiber, and other beneficial nutrients, grape pomace is increasingly incorporated into food production to enhance the nutritional profile of products like bread, cereals, pasta, and even meats and seafood.
- Grape waste can be distilled into alcoholic beverages like grappa, transformed into biofuel through the extraction of useful compounds, and turned into culinary items such as cookies, flour, and oils.
To produce a standard 750 milliliter bottle of wine, approximately 2.6 pounds (1.17 kilograms) of grapes are required. After pressing, about 20% of that weight remains as grape skins, seeds, and stems. According to a 2016 article in the journal Comprehensive Reviews in Food Science and Food Safety, the global wine industry generates nearly 12 million tons (11 million metric tons) of grape waste, known as pomace (or grape marc), annually.
So, how do wineries handle all of this leftover material? You might assume that disposing of such large amounts would pose a sticky issue. However, despite the liquid being pressed out, the remaining substance has multiple potential uses.
As highlighted in a 2005 article from Wine Maker magazine, the composition of pomace varies depending on the type of wine produced and the timing of liquid extraction. For white wine, the juice is extracted before fermentation, leaving pomace rich in sugars, nitrogen, and amino acids. In contrast, red wine pomace, which is pressed after fermentation, has lower sugar content and fewer tannins, the compounds responsible for bitterness. Nonetheless, fermented pomace still contains a wide range of components, including cellulose, tartaric acid, other organic acids, sugars, tannins, plant pigments, and aromatic compounds.
One method of utilizing pomace is to distill it into other alcoholic beverages. For instance, pomace from white wine can be distilled into grappa, a traditional Italian brandy. (Here’s an article from Life in Italy exploring the history of this drink.)
Pomace has traditionally been repurposed as fertilizer or animal feed, but scientists are increasingly focused on researching ways to extract valuable components from grape marc for use in applications such as fuel alcohol and biofuel production, as well as the creation of biosurfactants for environmental cleanup efforts.
Researchers in food science have found that pomace is packed with beneficial nutrients like antioxidants, fiber, and compounds that help control blood sugar levels and promote feelings of fullness. These elements make it an excellent addition to many foods, enhancing their health benefits. Pomace is now being used as an ingredient in products such as bread, cereal, pasta, cheese, ice cream, and even in meats and seafood.
In northern California's wine region, some wineries, as reported in a 2015 article from the Sonoma Press Democrat, have started using pomace to create cookies, flour, and even culinary oils.
The Republic of Tea, a renowned premium tea company, offers a unique tea made from the skins of wine grapes.
