Influence of valine and other amino acids on total diacetyl and 2,3-pentanedione levels during fermentation of brewer's wort

Abstract

Undesirable butter-tasting vicinal diketones are produced as by-products of valine and isoleucine biosynthesis during wort fermentation. One promising method of decreasing diacetyl production is through control of wort valine content since valine is involved in feedback inhibition of enzymes controlling the formation of diacetyl precursors. Here, the influence of valine supplementation, wort amino acid profile and free amino nitrogen content on diacetyl formation during wort fermentation with the lager yeast Saccharomyces pastorianus was investigated. Valine supplementation (100 to 300 mg L(-1)) resulted in decreased maximum diacetyl concentrations (up to 37 % lower) and diacetyl concentrations at the end of fermentation (up to 33 % lower) in all trials. Composition of the amino acid spectrum of the wort also had an impact on diacetyl and 2,3-pentanedione production during fermentation. No direct correlation between the wort amino acid concentrations and diacetyl production was found, but rather a negative correlation between the uptake rate of valine (and also other branched-chain amino acids) and diacetyl production. Fermentation performance and yeast growth were unaffected by supplementations. Amino acid addition had a minor effect on higher alcohol and ester composition, suggesting that high levels of supplementation could affect the flavour profile of the beer. Modifying amino acid profile of wort, especially with respect to valine and the other branched-chain amino acids, may be an effective way of decreasing the amount of diacetyl formed during fermentation.

Fig. 1

a The ethanol content (% v/v; solid line) and real extract (weight %; dashed line), and b yeast dry mass (in gram per litre; solid line) and pH (dashed line) of the worts supplemented with various amounts of valine as a function of fermentation time (hour). Values are means from two independent fermentations. Error bars where visible represent the range

Fig. 2

The a diacetyl and b 2,3-pentanedione concentrations (in microgram per litre) of the worts supplemented with various amounts of valine as a function of fermentation time (in hour). The dotted lines at 100 and 900 μg L⁻¹ depicts the flavour threshold (Meilgaard 1975). Values are means from two independent fermentations. Error bars where visible represent the range

Fig. 3

a The ethanol content (% v/v; solid line) and real extract (weight %; dashed line), and b yeast dry mass (in microgram per litre; solid line) and pH (dashed line) of the all-malt (Standard FAN) and semi-synthetic (Reduced FAN) worts supplemented with valine as a function of fermentation time (in hour). Values are means from two independent fermentations. Error bars where visible represent the range

Fig. 4

The a diacetyl and b 2,3-pentanedione concentrations (in microgram per litre) of the all-malt (Standard FAN) and semi-synthetic (Reduced FAN) worts supplemented with valine as a function of fermentation time (in hour). The dotted lines at 100 and 900 μg L⁻¹ depicts the flavour threshold (Meilgaard 1975). Values are means from two independent fermentations. Error bars where visible represent the range

Fig. 5

The change in valine concentration (in milligram per litre per hour) and diacetyl concentration (in microgram per litre per hour) of the all-malt (Standard FAN) worts supplemented with valine as a function of fermentation time (in hour). Values are means from two independent fermentations

Fig. 6

The (a, c, e) diacetyl and (b, d, f) 2,3-pentanedione concentrations (in microgram per litre) of the worts supplemented with various groups of amino acids as a function of fermentation time (in hour). The dotted lines at 100 and 900 μg L⁻¹ depict the flavour threshold (Meilgaard 1975). Values are means from two independent fermentations. Error bars where visible represent the range

Fig. 7

The change in valine concentration (in milligram per litre per hour) and diacetyl concentration (in microgram per litre per hour) of the worts supplemented with various groups of amino acids as a function of fermentation time (in hour). Values are means from two independent fermentations