Lesson 6 - Microorganism Detection and Control

Welcome back. So, what were your thoughts?

You will be keen to predict the stability of your product and can use simple forcing tests to check this. During the normal ageing process, contaminants grow slowly, eventually causing turbidity and spoiling the product. A forcing test aims to accelerate this process, by storing samples of the packaged bottles and kegs in warm conditions for a period of time. The product is then examined for turbidity and tasted.

Naturally such processes have their drawbacks. There is no enrichment in the sample, and you need to find a warm storage area. A temperature of 27 °C is a good bet for accelerating growth of the LAB and the Gram-negative anaerobic spoilers Pectinatus and Megasphaera. Whilst your bottles can be examined non-destructively daily, you will need to select a timescale to broach your kegs for assessment. If you do pick up spoilage, you will not know where it originated or what the offending microorganisms are, although their flavour-active metabolic compounds in your beer can certainly give you a clue!

Even with a fully equipped microbiology laboratory, traditional methods of detection have their limitations. Let us summarise these:

• Initial tests may not identify the offending microorganisms and their point of ingress
• Many microorganisms are fastidious, and do not grow well or at all on the culture media, even with enrichment media
• The brewery needs a lot of different specialist media
• Preparing media and interpreting results is a specialist skill
• The traditional methods are time consuming, limiting reaction countermeasures

As a consequence, a multitude of new methods have been developed to address these drawbacks.