MEASUREMENT AND PREDICTION OF THE SUSCEPTIBILITY OF LAGER BEER TO SPOILAGE BY LACTIC-ACID BACTERIA

The ability of 14 strains of hop-resistant lactic acid bacteria (Lacto bacillus spp., Pediococcus spp.) to grow in 17 different lager beers w as assessed using a biological challenge test. All beers were spoiled by at least one strain: all strains could grow in at least one beer. T he sensitivity of different beers to spoilage by lactic acid bacteria varied. Spoilage potential could be described in the form of a 'Resist ance to Spoilage Value' (RSV) based on the ability of the organisms to grow in each beer. Parameters which correlated to RSV included pH, be er colour and the content of free amino nitrogen, total soluble nitrog en, a range of individual amino acids, maltotriose and the undissociat ed forms of SO2 and hop bitter acids. Predictive models based on the t echnique of partial least squares regression and constructed using val ues for undissociated SO2 content, undissociated hop bitter acids cont ent, polyphenol content, maltotriose content, free amino nitrogen cont ent and a colour intensity component allowed RSV to be predicted.