A Comparative Study of Malthouse and Brewhouse Microflora

Abstract

The microflora of malting and mashing was investigated with emphasis on the numbers and types of lactic acid bacteria (LAB)present during these processes. A traditional small-scale floor malthouse, a modern, pneumatic large-scale malthouse and two brewhouses, each of which were utilised for the manufacture of stout and lager brews were studied. The bacterial population of dried, stored barley for malting was dominated by Gram — coliforms and pseudomonads, with LAB constituting a small minority of the total viable count. In both malthouses, the microbial count increased dramatically during barley steeping. Although pseudomonads still dominated, a significant increase in the LAB population was observed. Viable counts decreased slightly towards the end of germination and were reduced by >98% for all groups during kilning. Final counts of LAB on the kilned and screened malt were approximately 105, comprising 0.5% of the total viable microbial count. While leuconostocs were the predominant LAB detected in the early stages of the process, there was a discernible shift towards homo-fermentative lactobacilli during barley germination. Viable counts of LAB during lager and stout brewhouse mashes in two breweries indicated that initial microbial counts after mashing-in were high (from 105-107 CFU/g) and these decreased steadily during the mash programme. In the initial stages of mashing, the LAB population consisted of an equal mixture of lactobacilli and pediococci, but lactobacilli dominated the later stages of the mash. The pre-lauter viable count of LAB was generally <10 CFU/g.