The role of nitrogenous components in malt and wort during the production of beer has long been recognized. The concentration and range of wort amino acids impact on ethanolic fermentation by yeast and on the production of a range of flavour and aroma compounds in the final beer. This review summarizes research on Free Amino Nitrogen (FAN) within brewing, including various methods of analysis.

The Free Amino Nitrogen (FAN) content of wort prescribes efficient yeast cell growth and fermentation performance. FAN consists of the individual amino acids, small peptides and ammonia ions formed during malting, the relative amounts of which vary. In this paper, the individual constituents of FAN were dissected and their effect on both ale and lager fermentations determined. The patterns of amino acid and small peptide uptake and the changes in extracellular protease activity revealed the dynamic environment that develops during fermentation. Lysine and methionine, previously identified as key amino acids in wort fermentation, were investigated further.

The utilisation of small peptides by brewing yeast is poorly understood despite a wealth of information on peptide transport by other microorganisms. A novel method for detection, isolation and measurement of small peptides during brewery wort fermentations was used to monitor utilisation by ale and lager yeast strains. Oligopeptide levels in wort were found to fluctuate throughout the fermentations. Measurement of extracellular protease activity provided evidence that yeast are able to continually regulate protease production in order to break down wort polypeptides into utilisable nitrogeneous materials.

Progress during the past 25 years regarding our knowledge of brewer's yeast strains is considered. This is not a comprehensive review but rather focuses on some specific areas. These areas include a brief description of genomics, proteomics and metabolomics as applied to brewer's yeast strains. This review subsequently considers differences between ale and lager yeast strains, the uptake and metabolism of wort sugars and amino acids, yeast flocculation, yeast management between fermentations and yeast strain genetic stability. The question of process intensification, with particular attention to highgravity brewing, is also addressed. Fermentation systems and processes are considered with an emphasis on novel procedures for stirred fermentations.

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The occurrence of beer spoilage bacteria belonging to the genera Pectinatus and Megasphaera in ten major UK breweries was investigated. The sampling points were selected from fermentation areas, beer conditioning areas and beer bottling and canning sites. Multiplex PCR methodology was used for detection of three Pectinatus and three Megasphaera species using speciesspecific primers. The presence of six Lactobacillus species was also examined. Overall, 117 samples were analysed from ten breweries; six samples were positive for the presence of Pectinatus species and three samples were positive for the presence of Megasphaera species, while 34 samples were positive for the presence of Lactobacillus species. Lactobacillus species appeared to be the major potential spoilage microorganisms. Although none of the actual beer samples were found to be positive for Pectinatus and Megasphaera species, their occurrence in aerobic brewery environments indicates sanitation problems and revealed the presence of highly established biofilms in some breweries.

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