The increasing demand for sustainable and health-conscious fermented beverages has positioned sour beer as a compelling product for innovation. Apple pomace from “Golden Delicious” and “Pinova” varieties was sourced from a local orchard in Cluj-Napoca, Romania (46°48′23.26″N 23°35′18.05″E), and incorporated during wort boiling at ratios of 1:3, 1:5, and 1:10 (pomace to wort). Two fermentation approaches were employed: pre-fermentation with Levilactobacillus brevis, followed by alcoholic fermentation with Saccharomyces cerevisiae, and co-fermentation with both strains simultaneously. Control samples for both fermentation strategies were also made.

Fermentation kinetics were monitored through standard physicochemical parameters. Results showed that the presence of apple pomace contributes to a more pronounced acidification, as evidenced by a decrease in pH (from 4.25 to 4.06 in co-fermented samples and from 3.83 to 3.60 in the pre-fermented ones) and an increase in total titratable acidity (from 4.1 to 5.04 g/L lactic acid in pre-fermented conditions and from 2.5 to 3.01 g/L lactic acid in the co-fermented conditions). Regarding the alcohol content, the samples with pre-fermentation conditions and apple pomace had the lowest concentration (6.31 ± 0.04% ABV), but they had the highest value for total acidity (5.04 ± 0.07 g/L lactic acid). Apple pomace also affected the colour of the sour beer, making it lighter (from 15 EBC to 9 EBC in co-fermented conditions and from 13 EBC to 8 EBC in pre-fermented ones). The total polyphenol content was slightly higher in the co-fermented sour beers (0.459 mg GAE/mL) compared with pre-fermented beers (0.442 mg GAE/mL). The use of apple pomace from a local juice and cider producer supports sustainability by reducing food waste and promoting the circular use of local agro-resources. From a safety perspective, all fermentations were carried out under controlled conditions, ensuring the exclusion of contamination or spoilage.

Acknowledgments: This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CCCDI - UEFISCDI, project number PN-IV-P7-7.1-PED-2024-0800, within PNCDI IV.