MODELING GROWTH AND OFF-FLAVORS PRODUCTION OF SPOILED BEER BACTERIA, PECTINATUS-FRISINGENSIS

The genus Pectinatus includes strictly anaerobic Gram-negative non-spore-forming mesophilic bacteria often referred to as beer-spoilage bacteria. Pectinatus frisingensis was chosen as the reference strain. The organisms were grown in batch cultures under stringent anaerobic conditions in a synthetic medium and with pH regulation. Various glucose and lactate concentrations were used, and a low inoculum reproduced spoilage conditions in bottled beer. Propionate and acetate are the major compounds responsible for the off-flavour of beer. Gompertz curves were fitted to acid-biomass production and glucose consumption; thereby the lag-phase, production rate and final concentrations were derived. Volatile fatty acids production began 19 h after biomass growth. There was no linear effect of substrate on final concentration of propionate, acetate and biomass. An additive model is proposed for the prediction of bacterial growth and acid production on both glucose and lactate.