A comparative study of malthouse and brewhouse microflora

The microflora of malting and mashing was investigated with emphasis on the numbers and types of lactic acid bacteria (LAB) present during these proce sses. A traditional small-scale floor malthouse, a modern, pneumatic large- scale malthouse and two brewhouses, each of which were utilised for the man ufacture of stout and lager brews were studied. The bacterial population of dried, stored barley for malting was dominated by Gram - coliforms and pse udomonads, with LAB constituting a small minority of the total viable count . In both malthouses, the microbial count increased dramatically during bar ley steeping. Although pseudomonads still dominated, a significant increase in the LAB population was observed. Viable counts decreased slightly towar ds the end of germination and were reduced by >98% for all groups during ki lning. Final counts of LAB on the kilned and screened malt were approximate ly 10(5), comprising 0.5% of the total viable microbial count. While leucon ostocs were the predominant LAB detected in the early stages of the process , there was a discernible shift towards homo-fermentative lactobacilli duri ng barley germination. Viable counts of LAB during lager and stout brewhous e mashes in true breweries indicated that initial microbial counts after ma shing-in were high (from 10(5)-10(7) CFU/g) and these decreased steadily du ring the mash programme. In the initial stages of mashing, the LAB populati on consisted of an equal mixture of lactobacilli and pediococci, but lactob acilli dominated the later stages of the mash. The pre-lauter viable count of LAB was generally <10 CFU/g.