Production of grape marc kombucha: Valorization of a wine by-product

The revalorization of by-products is a priority for sustainable winemaking. This study explores the potential of white grape marc as a raw material for producing a kombucha-style beverage. We compared the fermentation processes of traditional tea kombuchas (green and black) and grape marc kombucha (Grape-K), all fermented with a homemade Symbiotic Culture of Bacteria and Yeast (SCOBY) cultured in grape marc infusion. The results demonstrated comparable acid production across all variants, with Grape-K showing enhanced sugar consumption. The microbial community was primarily composed by Brettanomyces bruxellensis (yeast) , Oenococcus oeni and Liquorilactobacillus ghanensis (lactic acid bacteria), and Komagataeibacter intermedius (acetic acid bacteria). Although Grape-K contained lower levels of phenolic compounds and higher acetic acid concentrations than tea-based kombuchas, it exhibited a significant increase in antioxidant activity post-fermentation. Using Muscat grape marcs, known for their enhanced floral notes, improved the organoleptic profile of the beverage. The balance of volatile acidity with other aromatic compounds in Grape-K highlights the potential of grape marc, especially from aromatic white varieties, as a promising raw material for creating kombuchas with distinct and appealing aromatic profiles. • Grape marc kombucha showed similar pH and higher sugar consumption than tea kombucha. • Microbial composition of the three kombucha was similar in number and isolated genera • Grape marc kombucha increased its antioxidant capacity post-fermentation. • The three kombucha products were organoleptically different. • Grape marc kombucha was the preferred choice by tasters.