Low-temperature brewing by freeze-dried immobilized cells

We propose a novel biocatalyst in brewing. A cryotolerant strain of Saccharomyces cerevisiae was immobilized on delignified cellulosic material followed by freeze-drying of the immobilized cells without the use of any cryoprotectant. The freeze-dried immobilized biocatalyst was used in repeated-batch fermentation of wort and showed reduced fermentation time and increased productivities as compared with free freeze-dried cells (FFDCs). It also demonstrated suitability for low-temperature brewing (5 and 0degrees). The fermentation time in repeated-batch fermentations at 15degreesC was 1.5-2 d for a period of 13 mo, showing a high operational stability of the system. At 0degreesC the freeze-dried immobilized biocatalyst showed a 2- to 3.5-fold decrease in fermentation time in comparison with FFDCs. Polyphenol contents, bitterness, and diacetyl concentration were lower in beers produced by freeze-dried immobilized cells as compared with FFDCs. At 0degreesC polyphenols were 40% lower than at 15degreesC. Higher alcohols were reduced and ethyl acetate increased in comparison with FFDCs. Amyl alcohols at 0degreesC were lower than half of their content at 15degreesC, while ethyl acetate was 31 mg/L at 0degreesC and 18 mg/L at 15'C. These data justify the improved aroma and taste of beers produced by freeze-dried immobilized biocatalyst mainly at low temperatures.