Studies on the Uptake and Metabolism of Wort Sugars During Brewing Fermentations

Abstract

Brewers' wort contains five fermentable sugars: glucose, fructose, sucrose, maltose, and maltotriose. In most worts, maltose is the highest concentration, followed by maltotriose and glucose. These sugars are taken up by yeast in a distinct order (or priority), with glucose repressing the uptake of maltose and maltotriose. Glucose is taken up without the expenditure of yeast metabolic energy, whereas maltose and maltotriose uptake requires energy (active transport). The concentration of each sugar, together with their relative proportions to one another, influence overall wort fermentation rate and extent. There are also differences between ale and lager yeast strains with respect to wort sugar uptake characteristics. For example, ale strains are less able to utilize won maltotriose than lager strains. In addition, the concentration of wort glucose and maltose influence beer flavor. In particular, won with elevated levels of glucose produces beers with high concentrations of esters (particularly ethyl acetate and isoamyl acetate). Worts containing high levels of maltose, however, produce beers with much reduced concentrations of these esters. This is particularly the case with high-gravity worts (>16°Plato).