Elucidation of the Polygenic Basis of Efficient Maltotriose Fermentation and its Variation among Brewing Yeast Strains

The brewing, baking and bioethanol industries rely on the rapid and efficient fermentation by selected yeast strains of hydrolysatesrich in glucose and the a-glucosides maltose and maltotriose. In the brewing industry, the latter two sugars are predominant. Besides maltose (50-60%), maltotriose (15-20%) and glucose (10-15%), an all-malt brewer#s wort also contains trace amounts of fructose and sucrose. Although some overlap occurs, brewing yeast strains will utilize glucose, fructose, maltose and maltotriose in this order. Unlike maltose, which is easily fermented by most yeast strains after glucose depletion, maltotriose fermentation is often incomplete, variable or even absent [20,73]. The inability to ferment maltotriose in a rapid and complete manner leads to sluggish fermentations leaving a high residue of fermentable sugar, mainly maltotriose, in the finished beer. This results in beer with a too high calorie content. It also results in lower ethanol yields and atypical beer flavour profiles. The aim of the present project is to identify the genetic basis of efficient maltotriose fermentation using the well-established technology platform for polygenic analysis and to determine the variation in the causative genes among commercial brewing yeast strains.