Sequentially Pitching Lactic Acid Bacteria and Active Dry Yeasts for Sour Beer Production

Abstract

Lactic acid bacteria are key constituents in the souring process of traditional acidic beers, resulting from spontaneous or mixed fermentations. The development of such beer styles provides a balanced and complex-flavored beverage but is time-consuming and not easily repeatable. New time-efficient alternatives include successively pitching a souring bacteria and yeast, such that both have optimal fermentation conditions. In this study, each microorganism is assessed to comprehend its individual impact on the fermentation process (acidification and fermentation rates, attenuation, ethanol production) and its influence on physicochemical and organoleptic parameters. Lactic acid bacteria are responsible for the wort’s acidification, reaching a pH of 3.5 within 48 h, by converting up to 5 g/L of simple sugars into organic acids and other by-products. The two-step acidification and fermentation process alters the color and bitterness, the latter decreasing from an initial iso-α-acid concentration of 29 mg/L to an average of 13 mg/L. The sequential method shows that the decarboxylation and subsequent reduction of hydroxycinnamic acid precursors into their vinyl and ethyl derivatives is strain dependent. All tested lactic acid bacteria appear to possess the decarboxylation enzymes. However, only Lactiplantibacillus plantarum can reduce vinylphenols into ethylphenols.