The Role of Small Wort Peptides in Brewing Fermentations

Abstract

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.

Variation in gluten protein and peptide concentrations in Belgian barley malt beers

“…During the malting and mashing processes, activated barley endogenous proteinases hydrolyse gluten partially to peptides or completely to amino acids . Much of this proteinaceous material in wort is removed during the brewing process, with the spent grains and hot‐break, or is taken up by yeast during fermentation for nitrogen metabolism . The gluten protein and peptide balance throughout the brewing process of an all‐barley malt beer was monitored by Dostálek et al and Guerdrum and Bamforth .…”

The Production of Secondary Metabolites with Flavour Potential during Brewing and Distilling Wort Fermentations

“…Regulation of higher alcohol biosynthesis is complex since they either have been produced as by-products of amino acid metabolism or via pyruvate and ethanol produced from carbohydrate metabolism (Figures 1 and 2) [39]. Table 4) [40,41] from which they take the amino group (Ehrlich Pathway) so that they can be incorporated into their own structures. What remains from the amino acids are α-keto acids which enter into an irreversible chain reaction that will ultimately form higher alcohols.…”

“…As ammonia was not detected in the medium, it was assumed that it was incorporated directly into yeast proteins. Subsequently, Neubauer and Fromherz [42] proposed a few intermediate steps to the Ehrlich Table 4) [40,41] from which they take the amino group (Ehrlich Pathway) so that they can be incorporated into their own structures. What remains from the amino acids are α-keto acids which enter into an irreversible chain reaction that will ultimately form higher alcohols.…”

“…The same series of fermentation trials showed that when wort FAN levels were reduced, diacetyl production was also decreased. This effect is presumably due to faster absorption of preferred amino acids [40,41,46], resulting in an earlier and enhanced demand for valine and its increased uptake due to less competition for amino acid permease interactions. Increased background levels of initial wort amino acids (maintaining the valine concentration constant) resulting in greater production of diacetyl.…”

Comparison of fermentation results and quality of the agricultural distillates obtained by application of commercial amylolytic preparations and cereal malts

“…Nitrogen uptake slows or ceases later in the fermentation as yeast multiplication stops. When the sugar content is high and vital nutrients are lacking, a stuck fermentation can occur [46,47].…”