Grape pomace is the solid material left over after grapes are crushed and pressed during winemaking. It consists of the skins, seeds, and stems that remain once the juice has been extracted. The global wine industry produces an estimated 10.5 to 13.1 million tons of this byproduct every year, and what was once treated as waste is now recognized as a surprisingly nutrient-dense material with growing applications in food, agriculture, skincare, and environmental science.
What Grape Pomace Contains
The defining feature of grape pomace is its fiber content, which ranges from 43% to 75% of the total dry weight. That fiber is a mix of cellulose, hemicellulose, pectin, and lignin. Lignin alone accounts for roughly 17% to 24% of the pomace. Protein content is relatively low, sitting below 4%.
The seeds within the pomace carry their own distinct profile: 34% to 36% oil, 4% to 6% tannins, and 10% to 28% cellulose depending on the variety. This seed oil is rich in polyunsaturated fatty acids, which partly explains why grape seed oil became a popular cooking and cosmetic ingredient.
Beyond the basic macronutrients, grape pomace is loaded with phenolic compounds, the same plant chemicals responsible for the color, flavor, and supposed health benefits of red wine. These fall into two broad families: flavonoids and non-flavonoids. The major players include anthocyanins (the pigments that make red grapes red), catechins, procyanidins (condensed tannins found mainly in the seeds), quercetin, gallic acid, and resveratrol. Resveratrol levels in pomace typically range from about 0.10 to 0.98 mg per 100 grams, though certain varieties like Cabernet Sauvignon can reach 4 to 9 mg per 100 grams.
Red vs. White Grape Pomace
The most obvious difference between red and white grape pomace is color, and that difference comes down to anthocyanins. Red grape pomace contains up to 13 different anthocyanins; white grape pomace contains essentially none. Beyond that single distinction, researchers screening pomace from multiple grape varieties found no principal chemical differences between red and white types. Both contain similar profiles of phenolic acids, catechins, flavonols, and stilbenes. The skins of both are rich in hydroxycinnamic acids and flavonol glycosides, while the seeds in both are concentrated sources of flavanols.
Why It Matters for the Environment
Dumping millions of tons of grape pomace into landfills or spreading it directly on fields creates real environmental problems. As the material decomposes, it produces methane, a potent greenhouse gas. Large-scale disposal can also acidify soil and pollute waterways, because the high concentration of tannins and organic acids in pomace can leach into groundwater and disrupt local ecosystems. These concerns have pushed the wine industry and researchers to find productive ways to use pomace rather than discard it.
Use in Animal Feed
One of the most established uses for grape pomace is as a feed ingredient for livestock, particularly cattle. Adding it to diets at moderate levels (around 15% of total dry matter) offers several advantages. The polyphenols in pomace shift nitrogen excretion from urine to feces, which reduces ammonia and other reactive nitrogen emissions from manure. Studies on cattle have also shown that including 27% to 30% dried or ensiled grape pomace in diets can decrease methane emissions by altering gut microbial communities. On top of that, animals fed pomace at 10% to 58% of their diet have shown increased levels of beneficial polyunsaturated fatty acids in their meat, along with better antioxidant capacity.
There are limits, though. Grape pomace is very high in lignin, with acid detergent lignin measured at about 34.5% of dry matter in some samples. Lignin physically blocks digestive enzymes from reaching the cellulose and hemicellulose in fiber, which slows digestion and makes animals feel full before they’ve absorbed enough nutrients. In feedlot heifers, pushing pomace above 15% of the diet reduced the digestibility of fiber, protein, and overall dry matter. At 30%, body weight gain and feed efficiency dropped noticeably. The tannins in pomace can also bind to proteins and limit microbial activity in the rumen, further restricting nutrient absorption at high inclusion levels.
Food Applications
Dried and ground into a powder, grape pomace is increasingly used as a functional ingredient in human food. Researchers have substituted grape pomace powder for wheat flour in bread at levels of 5% and 10%, producing loaves with significantly higher fiber and polyphenol content. The fortified bread retains acceptable texture and taste while delivering compounds associated with antioxidant activity. Similar experiments have been conducted with cookies, pasta, and other baked goods, all aiming to add nutritional value to everyday staples using what would otherwise be industrial waste.
The appeal is straightforward: grape pomace powder adds fiber and plant compounds without requiring any novel processing. It can be produced simply by drying and milling the leftover pomace, making it an accessible ingredient for food manufacturers looking to create “enriched” or “fortified” products.
Skincare and Cosmetics
The same antioxidant compounds that make grape pomace interesting as a food ingredient have drawn attention from the cosmetics industry. Pomace extracts are rich in polyphenols, flavonoids, anthocyanins, and vitamin C, all of which help neutralize free radicals and protect skin cells from oxidative stress.
In laboratory studies, pomace extracts have been shown to protect fibroblasts, the cells responsible for producing collagen, elastin, and hyaluronic acid. Compounds like catechins, procyanidins, and resveratrol inhibit enzymes that break down collagen and elastin, helping preserve skin firmness. Grape seed extract specifically has demonstrated the ability to protect skin cells against UV-induced oxidative damage. Resveratrol promotes wound healing by stimulating fibroblast movement and growth while reducing harmful reactive oxygen species. One study found that extract from the Regent grape variety, applied at a concentration of 25 micrograms per milliliter, significantly increased fibroblast survival and skin regeneration rates, effects tied to its particularly high flavonoid content.
These properties position grape pomace as a source of natural anti-aging and regenerative ingredients, and extracts from it are already appearing in serums, creams, and masks marketed for hydration, elasticity, and photoprotection.