Winemaking choices shape the value of grape pomace

The way wine is made can cause the value of grape pomace to vary severalfold, researchers at the Estonian University of Life Sciences have found, ERR reports. The residue can be used to age cheese or make spirits, but it spoils quickly, so its storage or further use needs to be planned during winemaking.

Pomace makes up 15 to 30 percent of the mass of grapes processed, depending on the method. Only a small share is reused worldwide, mainly as animal feed, for making spirits or as compost. It contains bioactive compounds that could make it a raw material for new products rather than waste.

In Estonia, one example of reuse is Viinamärdi farm in Tartu County, where local grape pomace has been used to age Pecorello Brillo sheep’s cheese. Pomace is also increasingly distilled into spirits known in Italy as grappa and in Georgia as chacha. Estonia does not yet have a widely used name for the drink, researcher Kersti Seeme said. The distillate can also be used to make fortified wines, including those produced using a method similar to port.

Seeme, a junior researcher in food science at the university, led the study published in the Proceedings of the Estonian Academy of Sciences. She worked with professor Kadri Karp, chair of the university’s horticulture department, and senior lecturer Reelika Rätsep, who specialises in plant-based food technology.

The team studied two dark-skinned hybrid grape varieties grown at the university’s Rõhu experimental station near Tartu: Hasansky Sladky, originally from Ukraine, and Zilga, bred in Latvia. Both are adapted to cooler climates. Earlier research found that pomace from hybrid grapes grown in Estonia has levels of polyphenols and antioxidant activity comparable to, or higher than, those in residues from processing other fruits.

Since 2021, Estonia has been part of the European Union’s wine-growing Zone A, which allows wine to be produced and sold in the country. Winemaking has since become more popular among small producers, though production remains modest. Estonian vineyards grow 15 varieties; total wine production was 5,872 litres in 2022 and 5,000 litres in 2023. The most widely grown variety is the white Solaris, followed by the dark varieties Rondo, Zilga and Hasansky Sladky.