Factors influencing the flavour stability of pale lagers are discussed with particular reference to the enzymic oxidation of fatty acids, one of the principal reactions contributing to the development of off-flavours in aging beer. As pale lager malt is very lightly kilned, lipoxygenase (the enzyme of fatty acid oxidation) is not always entirely inactivated, so that some oxidation of fatty acids can take place during milling and the early stages of mashing. Moreover, these malts contain lower levels of natural antioxidants than darker malts. The optimization of brewhouse operations, the fermentative performance of the yeast, post fermentation treatment, packaging and distribution with regard to flavour stability is discussed. It is pointed out that while there are established quality standards for green malt with regard to the relevant parameters, no such standards have been specified for kilned malt with regard to such factors as residual microorganisms and products of microbial metabolism, pH, lipoxygenase activity, hydroperoxides content, etc., although these parameters are considered to be very significant in relation to the flavour stability of beer, and also that while the aliphatic aldehydes which play a key role in the formation of certain off flavours are very difficult to remove once formed, their formation can be prevented by appropriate measures in the brewhouse.
Keywords : beer brewing enzymic activity fatty acid inhibition lipoxygenase off flavour oxidation malt stability