Estimation of some fungi on stored barley

Abstract

Barley grain is converted to malt at the Heathcote, Canterbury, maltowrks of the Canterbury (N. Z.) Malting Company for New Zealand’s brewcries. The grain is harvested in the mid-summer months and must be stored in bags or bulk mid-summer months and must be stored in bags or bulk silos to ensure continuous supply of malt.

The Malting Company expressed concern that micro-organisms present on grain during storage may affect acceptability of malt for brewing. Malcolm (1968) briefly reviewed overseas instances in which malt made from weathered barley predisposed beer to gushing, a phenomenon of decreased gas stability. Fungal metabolites were implicated in this disorder by Prentice and Sloey (1960).

Further, in their review of carcinogens produced by fungi, Enomoto and Saito (1972) included reports of toxin production by some members of the genus Fusarium and by many species of Aspergillus and Penicillium, which have been frequently found on stored cereal foodstuffs. Their presence on barley for malting in New Zealand emphasises the need for further study of conditions of proliferation and possible harmful metabolite production by such fungi.

Thus, the present study was instigated to survey the microflora of stored barley and primarily to develop a technique or techniques for estimating the amount of fungus present on stored barley under given conditions.

In addition, techniques were sought which would give an estimation of the metabolic activity of fungi present at a level where they were not readily visible on the exterior of grains and outline the physical conditions of storage under which such fungi proliferated.

The project turned chiefly into a search for suitable estimation techniques using for test organisms, the five fungi most frequently isolated from stored barley. This approach was adopted in order to prevent some of the inconclusiveness to which estimations of mixed cultures of fungi would be subject and thus allow a clearer appraisal of each technique.