Effect of temperature on the formation of volatile by-products in brewing by immobilized cells

The formation of acetaldehyde, ethyl acetate, propanol-1, isobutanol amyl alcohols and methanol in repeated batch fermentations and continuous fermentations of wort, performed by a cryotolerant and alcohol resistant strain of Saccharomyces cerevisiae species, immobilized on delignified cellulosic (D.C.) material and gluten pellets was studied mainly at low temperatures. It was found that the fine and fruity aroma of beers obtained at lower temperatures may be attributed mainly to increase of % ethyl acetate on total volatiles determined and to decrease of amyl alcohols. D.C. material resulted to lower contents of higher alcohols in batch and continuous brewing as compared with gluten and free cells principally at low temperatures. AmyI alcohols and other higher alcohols were reduced in all cases (immobilized and free cells) as the temperature was decreased. Same change of amyl alcohols and other higher alcohols is reported in the case of gluten pellets as the temperature was reduced. However, their contents are higher than those of free cells. In general, comparing the contents of ethyl acetate from continuous and batch process, continuous resulted to higher values. In all cases, the flavor was remained stable for the long period of ten months storage.