Studies on the microbiology of barley malt production

Abstract

Populations of aerobic heterotrophic bacteria, niycelial fungi and yeasts occurring in the production of barley malt were examined by plating on agar media and by scanning electron microscopy. There was an increase in the total number of micro-organisms during germination of barley, although populations declined after kilning. Bacteria dominated numerically in all samples, with progressively lower populations of yeasts and filamentous fungi. There was no obvious pattern of spatial distribution of micro-organisms On/in the samples, although there appeared to be high populations of bacteria and fungal hyphae on the inner surface of kernels. The dominant groups of aerobic heterotrophic bacteria were presumptively identified as Alcaligenes sp., Arthrobacter globiformis, Clavibacter iranicuin, Erwinia herbicola, Lactobacillus spp. and Pseudomonas fluorescens. The principal filainentous fungi were Alternaria alternata, Aspergillus glaucus group, Cladosporium macrocarpum, Epicoccum purpurascens, Fusarium avenaceum, Geotrichum candidum and Penicillium spp. The yeasts isolated most frequently were Candida catenulata, Q.. vini, Debaryomyces hansenii, Hansenula polyniorpha, Kloeckera apiculata, Rhodotorula nrncilaginosa, Sporobolomyces roseus and Trichosporon bei gelii. Representative bacteria, mycelial fungi and yeasts were examined for the ability to degrade 8-glucan, starch or arabinoxylan. Approximately 50% of the fungi, <50% of the bacteria and <25% of the yeasts degraded these substrates. A culture filtrate of .. nivale demonstrated marked ability to reduce -glucan viscometrically and colorimetrically. The organism also degraded raffinose and sucrose. In micro-malting experiments the addition of Fusarium nivale and Geotrichum candidum did not produce substantial changes in terms of the physical and chemical characteristics of the finished malts.