Lesson 8 - Hygiene End of Unit SAQ

** Discuss the microorganisms that contaminate the raw materials used for brewing; describe the various threats they pose to both the brewer and consumer.

Response:

When discussing the contamination of raw materials, we should consider both the effect on beer appearance and flavour, as well as the subsequent health concerns.

Water

The water we use for making beer must be of a potable standard. Enterobacteriaceae, particularly the pathogenic species of Escherichia, Salmonella, Shigella and Yersinia all pose a threat to this. The faecal coliform, E. coli, is used as a proxy marker for determining sewage contamination of water. If detected in quantities that exceed specified standards, this should trigger immediate investigation.

Fortunately, the pathogenic Enterobacteriaceae will not grow in wort. However, the water may contain free-living coliforms such as Klebsiella, Enterobacter and Obesumbacterium, which can develop in wort. These are not, however, regarded as beer spoilage organisms.

Control should be exercised using regular microbial checking of the water supply and sterilisation of the product water used post-boil. This is often carried out using UV lamps. 

Malt/grains

Cereal grains (barley in particular), are susceptible to fungal infestation by moulds. This in turn produces harmful aflatoxins and mycotoxins, some of which are declared carcinogens. The level of the Fusarium marker, deoxynivalenol  (DON or vomitoxin), is usually specified by brewers and is regulated in many parts of the globe by authorities. DON is heat stable; it can survive boiling and persists in final beer, causing vomiting, diarrhoea, and haemorrhaging.

Hydrophobins are another non-toxic metabolite of Fusarium. These proteins cause gushing in beer, leading to consumer rejection.

Adjuncts

Liquid adjuncts, particularly high maltose syrups, are generally stored warm. This causes condensate to form, which collects on the syrup’s surface and creates a dilute sugar source. This can lead to butyric acid production from contaminating Clostridium bacteria. Butyric acid has an unpleasant ‘baby vomit’ aroma.

Hops

Poor storage, high temperature, and high moisture can lead to mould growth on hops. However, with modern practices such as pelletising under inert gas, alongside cold storage, these risks are minimal.

Yeast

If the brewery purchases yeast slurry or dried yeast there is a risk (typically small if the yeast is from reputable suppliers) that it could be contaminated with spoilage bacteria or wild yeast. Spoilage bacteria could affect fermentation and/or the beer in maturation and package causing off flavours and turbidity. Wild yeast would have the same effect and may also lead to over attenuation of the beer.