Sour Fruit Beers-Ethanol and Lactic Acid Fermentation in Beer Production.

Fruit and sour beers are popular due to their unique sensory characteristics. Owing to changes in physicochemical parameters, mixed culture fermentation is a promising research area. The aim of the study was to evaluate how ethanol and lactic acid fermentation, combined with the addition of berry fruits during the beer production process, influence the physicochemical and sensory characteristics of sour fruit beers. Three worts differing in hopping system were produced: one classic sweet wort and two lacto-fermented. Strawberries or raspberries were added to the young beer. This research showed that acidification of wort, fruit addition, and limiting of hopping time had a positive effect on both technological and sensory characteristics. Despite pH differences, alcohol content in beers was similar (2.52-3.21% v/v). Production method influenced mainly lactic acid (0-2.30 g/L), pH (3.53-4.79), and glycerol (0.83-1.62 g/L) contents. Non-acidified beers had the highest dextrin (17.64-23.13 g/L) and glycerol (1.36-1.62 g/L) levels. The addition of strawberries increased phenolics (205.21-237.03 mg GAE/L), FRAP (0.82-1.17 mmol TE/L), and refreshment sensation, while raspberries mainly enhanced sensory atributes (colour, foam, fruitiness, aroma). Lactic fermentation did not show a clear effect on polyphenol content or antioxidant activity. The research offers practical insights into functional beer development, with its novelty of using mixed fermentation and fruit addition to shape characteristics.