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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.

A new analytical method (liquid chromatography-antioxidant, LC-AOx) was used that is intended to separate beer polyphenols and to determine the potential antioxidant activity of these constituents after they were allowed to react online with a buffered solution of the radical cation 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS(•+)). Using the LC-AOx method, it was possible to demonstrate that the extent of the antioxidant activity was very much dependent on the phenolic compound considered. The method was also applied to the analysis of beer extracts and allowed the evaluation of their antioxidant activity at different steps of beer processing: brewing, boiling, and fermentation. This study showed that the total antioxidant activity remained unchanged throughout beer processing, as opposed to the polyphenolic content, which showed a 3-fold increase. Hopping and fermentation steps were the main causes of this increase. However, the increase measured after fermentation was attributed to a better extraction of polyphenols due to the presence of ethanol, rather than to a real increase in their content. Moreover, this method allowed the detection of three unknown antioxidant compounds, which accounted for 64 ± 4% of the total antioxidant activity of beer and were individually more efficient than caffeic acid and epicatechin.

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Radiolabelled glucose was added to a batch culture of Alcaligenes eutrophus during the accumulation of poly(3-hydroxybutyrate) (PHB) to label newly synthesized polymer. The specific radioactivity of the polymer continued to increase, by approximately 30%, after the cessation of PHB accumulation, indicating that turnover of PHB was occurring. Fractionation of PHB showed that high molecular mass polymer was gradually replaced by PHB of lower molecular mass. Turnover of PHB is the cause of the slow decline in the molecular mass of PHB following the cessation of polymer accumulation but is unlikely to be the sole reason for the more rapid decrease in the molecular mass of PHB during the accumulation phase.

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.

Iso-␣-acids and their chemically modified variants play a large role in evoking the bitter sensory attributes of lager character, but individual consumers may vary in their perception of bitterness. Sixteen lagers were scored in rank-rating for bitterness by 14 trained assessors and the concentrations of the six bitter components in these beers were determined by high performance liquid chromatography. Relationships between bitterness intensity and the bitter components were modelled well using partial least square regression with a correlation value of 0.92. When 8 assessors carried out time-intensity scoring of bitterness, profiles for single products were very different. However, single assessor profiles for multiple products showed qualitative similarities but quantitative differences. That individual assessors perceived bitter characters differently in relation to time has implications for new product development.

Key compounds in lager staling include furfural, hexanal, 5-hydroxymethyl furfural (5-HMF), and trans-2-nonenal. Quantitative data of headspace concentration in two lagers -one premium at 5% (abv), the other a standard product at 4% (abv) -were obtained by solid phase microextraction (SPME) followed by gas chromatography using a mass selective detector (GCMS). The concentrations of the aldehydes were used to predict overall stale scoring from sensory assessor data, of lagers stored at 4, 12, 30, and 37°C for 7, 14, 21 and 28 days. Concentrations of all four aldehydes increased with time of storage and with higher temperatures. Correlation coefficients for prediction of staleness in the premium lager were similar at 0.81 and 0.84 for partial least square regression (PLS1) and artificial neural network (ANN) modelling respectively, and the latter showed a lower root mean square error (RMS error). For the standard product, the correlation coefficients were 0.72 and 0.86, with ANN showing lower RMS error respectively. In both PLS models, E-2-nonenal had high regression coefficients and 5-HMF lower coefficients. Furfural and hexanal differed in contributions to the lagers.