Performance and osmotolerance of different strains of lager yeast in high gravity fermentations.

Jakobsen, M. and Piper, J.U.

Abstract
Studies were carried out on osmotolerance in laboratory media and performance in high gravity fermentations determined of brewing wort for widely used strains of lager yeast. Osmotolerance measured by the minimum water activity (aw) for growth did not vary significantly between the strains investigated. To relate findings to practical brewing, high gravity wort laboratory fermentations were carried out in brewery wort with 25% w/w sucrose adjunct, extract contents between 10 and 20% and at temperatures from 10 and 20 degrees C. Yeast performance of increasing extract contents and increasing temperatures varied between the strains investigated. Effects of increasing wort gravity and fermentation temperature on aroma components were observed in particular on esters, acetaldehyde and higher alcohols. Yeast growth pattern including flocculation and the ability to ferment high gravity worts varied amongst the strains. Yeast viability was severely reduced in yeast cells collected from fermentation of high gravity at high temperature.
Keywords : aroma fermentation high gravity brewing lager osmosis tolerance yeast