A comparison of rapid microbiological methods for detecting beer spoilage microorganisms.

Barney, M. and Kot, E.

Abstract
Unlike the pathogenic microorganisms for which rapid detection methods are widely and successfully used in medical diagnosis and food hygiene, many beer spoilage microorganisms grow slowly and require fairly specific conditions for satisfactory growth. Methods for direct detection without culturing, such as the direct epifluorescence technique (DEFT), polymerase chain reaction (PCR) and flow cytometry, can theoretically detect a single microorganism in a sample but in practice are labour intensive, difficult to automate and susceptible to various forms of interference which cause frequent errors. So called rapid indirect methods require a preliminary culturing to increase the cell numbers to a detectable level, so that the time required to ensure all organisms present are detected depends on the detection limit of the method and the growth rate of the slowest growing species likely to be present. Detection of beer spoilage microorganisms therefore requires 3 to 5 days using the impedance/conductance method, spectrophotometry or metabolite detection, or 2 to 3 days using ATP bioluminescence. Microcolony staining with computer enhanced image analysis and automatic counting can detect colonies of 100 to 1000 cells, which would require several more days to grow to a size visible to the naked eye, but is labour intensive and costly, while its automation still required much further development at the time of writing. A checklist of essential questions to be asked when considering the purchase of a rapid detection system for brewery use is presented.
Keywords : accelerated brewery contamination detection microorganism survey