Current practices in microbial monitoring in brewing rely heavily on conventional plate counts and forcing tests. Such tests, which require a sufficient time for microbial growth, provide a historical record, but are of limited use in process control. A primary need is for rapid and sensitive procedures which detect viable organisms. The means to distinguish organisms which can spoil from those which are benign, and the automation of procedures, are secondary considerations. Evaluating available methods for rapid microbial monitoring in the context of brewing industry requirements has identified areas for further development.

Cinnamic acid (100 ug ml"') incorporated in a solid medium was found to inhibit the growth of brewing strains (Pof~) of yeast while permitting the growth of Pof + wild yeast contaminants. Typically, colonies of Saccharomyces cerevisiae var. diastaticus (Pof+) mixed with brewing yeast (S. cerevisiae NCYC 240) were visible after 5d incubation at 25°C. The incubation time required to detect a selection of brewery wild yeast isolates was found to vary from 3-12 d.