Use of brewer's yeast expressing alpha-acetolactate decarboxylase in conventional and immobilized fermentations.

Linko, M., Suihko, M.-L., Kronlof, J. and Home, S.

Abstract
Fermentation trials using four recombinant brewers' yeast strains, transformed using the alpha acetolactate decarboxylase gene from either Klebsiella terrigena or Enterobacter aerogenes with either the ADH1 or PGK1 promoter in order to reduce the level of diacetyl formation, in both a conventional batch process and a continuous process in which the yeast was immobilized on porous glass beads, are described. All the transformed yeast strains performed well, producing beers of similar composition and flavour to those produced by the untransformed source strain. Diacetyl production was much lower than in the control fermentations, especially in the two yeasts in which the gene was expressed using the PGK1 promoter, allowing the maturation period to be much shortened or even eliminated.
Keywords : accelerated brewers' yeast diacetyl fermentation inhibition transformation yeast strain