Brewer's Yeast Propagation: The Basic Principles

Graham G. Stewart. International Centre for Brewing and Distilling (ICBD), Heriot-Watt University, Riccarton, Edinburgh, Scotland, EH14 4AS.
The concept of using a single brewing lager yeast strain was first introduced in 1883 together with a prototype propagation system. Similar developments with ale cultures occurred reluctantly many years later. The objective is to produce freshly propagated yeast culture biomass that it is not stressed, is vital and viable, and is free of contaminating microorganisms. The route to this objective requires a carefully designed sanitary propagation plant with an aeration/oxygenation system (either continuous or intermittent) that is able to supply sufficient oxygen to promote budding of the majority of yeast cells during their growth phase. The Pasteur and Crabtree effects are important concepts that influence yeast growth and fermentation procedures. The use of dried yeast in brewing is discussed and compared with its use in distilling and baking. To preserve yeast strain consistency and integrity, cultures should be maintained under accepted and well-tried culture collection conditions prior to propagation procedures beginning.

Keywords: Culture collections, Fermentation, Glycogen, Propagation, Stress, Trehalose, Wort (gravity and free amino nitrogen [FAN] concentration), Yeast (ale and lager)