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

The genus Pectinatus includes strictly anaerobic Gram-negative non-spo re-forming mesophilic bacteria often referred to as beer-spoilage bact eria. Pectinatus frisingensis was chosen as the reference strain. The organisms were grown in batch cultures under stringent anaerobic condi tions in a synthetic medium and with pH regulation. Various glucose an d lactate concentrations were used, and a low inoculum reproduced spoi lage conditions in bottled beer. Propionate and acetate are the major compounds responsible for the off-flavour of beer. Gompertz curves wer e fitted to acid-biomass production and glucose consumption; thereby t he lag-phase, production rate and final concentrations were derived. V olatile 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 predictio n of bacterial growth and acid production on both glucose and lactate.