The wine industry leaves behind an interesting coproduct which is called grape pomace. It consists of the solids that remain of grapes after they are pressed to remove its juice, and it contains the skins, pulp, seeds, and stems. In the alcohol beverage industry, water is added and allowed to ferment to produce “grappa”, a well-known alcoholic beverage originating in Italy.
Grape pomace is also used nowadays as a feedstuff for cattle, fertilizer, or to extract from its bioactive compounds such as polyphenols. Nearly nine million tons are produced annually around the world, with well-known wine regions being the main source of it. Its availability is not to be discounted since they constitute one fourth of the grape weight before its fermented into wine.
The dairy industry is well known for producing highly valued dairy products however it is also blamed for increasing the carbon footprint of agriculture. Industry coproducts such as grape pomace which are relatively inexpensive and need to be disposed-off in an environmentally friendly way are often used as feedstuffs in dairy cow diets. In addition, they are also considered not contributing significant volumes of greenhouse gases, since any emitted are mostly assigned to the primary product, in this case the alcohol beverages.
Grape pomace is rich in condensed tannins which have been shown to reduce methane production when fed to ruminants. In addition, these coproducts reduced in milk fat with higher proportions of polyunsaturated fatty acids which are beneficial to human health. In countries with grass-fed dairy systems and a strong wine industry, such as Australia, this coproduct is used to stretch the forage supply and not overgraze pastures during the dry months of the year.
In the US and particularly in the wine region of the west coast, the use of grape pomace has been also a tradition, mostly to reduce feed costs. There is not much information though on its nutritional value and its variability depending on the types of grapes used to make wine. As a result, there is also not enough research performed on its effect on dairy cow milk production. There’s not much research on its relatively high concentration of polyphenols and their impact on methane production emissions.