Low-temperature brewing by freeze-dried immobilized cells on gluten pellets

A biocatalyst, prepared by the immobilization of a cryotolerant strain of Saccharomyces cerevisiae on gluten pellets, was freeze-dried without any protecting medium and used for repeated batch fermentations of wort for each of the temperatures 15, 10, 5, and 0 degrees C. The fermentation time for freeze-dried immobilized cells was about 2-fold that of the corresponding time for wet immobilized cells on gluten pellets, and lower than the corresponding time for freeze-dried free cells, especially at 5 and 0 degrees C. Beers produced by freeze-dried immobilized cells contained alcohol levels in the range of 5.0-5.5% v/v, diacetyl concentrations lower than 0.5 mg/L, polyphenol concentrations lower than 145.5 mg/L, and free cell concentrations lower than 3 g/L. As a result, they had a very good clarity after the end of primary fermentation. The amounts of amyl alcohols were lower than 129.1 mg/L and reduced as the temperature was decreased. Ethyl acetate concentrations were found in the range of 22.1-29.2 mg/L, giving a very good aroma and taste in the produced beers.