Flavor formation and cell physiology during the production of alcohol-freebeer with immobilized Saccharomyces cerevisiae

Production of alcohol-free beer by limited fermentation is optimally perfor med in a packed-bed reactor operating in downflow. This ensures a highly co ntrollable system with optimal reactor design. In the present study, we rep ort on changes in the physiology of immobilized yeast cells in the reactor. During production, a simultaneous increase in the activity of alcohol acet yl transferase and formation of the esters ethyl acetate and isoamyl acetat e were observed In addition the amount of unsaturated fatty acids decreased significantly. Since these phenomena coincided with a significant decrease in growth rate, we conclude that the anaerobic conditions, and the absence of substantial levels of unsaturated fatty acids in wort limit cell growth during production and stimulate formation of acetate esters. Low temperatu res (2 degrees C) appeared to suppress production of alpha-acetolactate whe reas at 12 degrees C, substantial levels were obtained. An optimal and cons tant flavor profile of the alcohol-free beer can be achieved by introductio n of regular aerobic periods to stimulate yeast growth. Temperature can be used to control the rate of growth as well as the rate of flavor formation. (C) 1999 published by Elsevier Science Inc. All rights reserved.