Yeast Stress and Brewing Fermentations
Katherine A. Smart
from: Brewing Microbiology: Current Research, Omics and Microbial Ecology (Edited by: Nicholas A. Bokulich and Charles W. Bamforth). Caister Academic Press, U.K. (2017) Pages: 29-52.
A key performance indicator of brewing fermentations is the capacity of the yeast to convert wort into the desired fermentate in an appropriate timescale. Balancing the needs of the brewer and the yeast is more complex than is always appreciated. Brewery fermentations can impose a variety of stresses on the yeast cell, particularly when conducted at scale, and this is exacerbated by the use of serial repitching, in which the yeast is recycled to complete a number of successive fermentations. Brewing yeast strains are routinely exposed to fluctuations in oxygen concentration and the accumulation of carbon dioxide, hyperosmotic stresses which are wort gravity-dependent; pH downshifts during fermentation, which can be extreme if acid washing is applied between successive fermentations; accumulation of acetaldehyde, ethanol, and organic acids; nutrient abundance, imbalance, and scarcity; and temperature shifts from around 21°C to 2°C. This chapter will focus on some of the stresses that may be encountered during lager, ale, and where appropriate wheat beer fermentations conducted at scale read more ...