The problem of determining the correct level of pasteurisation for beer (i.e. the temperature/time combination which exposes the beer to just enough heat to be certain to kill off all spoilage microorganisms, and no more) is discussed. The difficulty lies in determining the degree of exposure to heat necessary to destroy or incapacitate the organisms in question. Methods of determining the heat resistance of microorganisms are discussed and the processes by which heat damages and destroys them are described together with the effects of water activity, sugars, lipids, pH, proteins, salts, the age and physiological condition of the cells, cell density, ethanol and carbon dioxide. (It is pointed out that, since ethanol enhances the effects of pasteurisation, low alcohol and alcohol free beers require more intense heating for microbiological stability and are therefore more prone to off flavours caused by overpasteurisation). The thermal resistance characteristics of lactic acid bacteria (genera Lactobacillus and Pediococcus), obligately anaerobic bacteria (Zymomonas, Pectinatus and Megasphaera), Hafnia protea (alias Flavobacterium proteus or Obesumbacterium proteus), the coliform bacteria (especially Enterobacter agglomerans), acetic acid bacteria (Acetomonas and Acetobacter) and yeasts (both brewing and wild strains) are discussed on the basis of a survey of the literature.
Keywords : beer contamination microorganism pasteurisation resistance survey