Ambient and low temperature winemaking by immobilized cells on brewer's spent grains: Effect on volatile composition

Repeated batch wine fermentations were conducted using immobilized yeast cells on brewer's spent grains as well as free cells, at 25, 20, 15 and 10 degrees C. The operational stability of the biocatalyst was good and no decrease of its activity was observed, even at 10 degrees C. Ethanol and wine productivities were high, showing the suitability of the biocatalyst for low temperature winemaking. The interaction effect of immobilization and temperature was statistically significant in most cases. Immobilized cells produced wines with a higher content of ethyl and acetate esters as well as volatile fatty acids, at temperatures of 15 and 10 degrees C, whereas the opposite was observed for free cells at higher temperatures. Same amounts of higher alcohols were produced by both immobilized and free cells. These amounts decreased dramatically with temperature drop. Wines produced by immobilized cells at low fermentation temperatures (10-15 degrees C) were characterized by a potentially better flavour due to a better ratio of esters to alcohols. (c) 2007 Elsevier Ltd. All rights reserved.