Sugar uptake and subsequent ester and higher alcohol production by Saccharomyces cerevisiae

The production of a number of esters and higher alcohols by brewing strains of Saccharomyces cereviaiae, in synthetic media containing only glucose, fructose or maltose as sole carbohydrate source, has been investigated. Results indicated that production of most volatiles was generally lower when maltose was the sugar being fermented, despite maltose-grown cells having higher viabilities and vitalities than glucose or fructose-grown cells. There was no significant difference in the levels of esters and higher alcohols produced during fermentation when glucose or fructose was metabolised, although strain variation was observed. Similar results were obtained when wort was supplemented with either glucose, fructose or maltose. Wort supplemented with maltose produced fewer volatiles, especially higher alcohols, than that which had a hexose sugar added. The activity of ester-synthesising enzymes present in glucose or maltose PYN grown cells was also examined. Similar levels of ethyl acetate and isoamyl acetate were obtained when cells grown in either glucose or maltose PYN were disrupted and ester production monitored. The implications of these results for the fermentation of high-gravity worts are discussed.