High gravity wort clarity and its effect on brewing yeast performance.

O'Connor-Cox, E.S.C., Lodolo, E.J., Steyn, G.J. and Axcell, B.C.

Abstract
Although many brewers prefer the wort to be clear at the time of pitching, others believe that cloudy worts are better for the fermentative performance of the yeast, partly because of the presence in them of substances regarded as important yeast nutrients (particularly lipids) and partly because it is thought that particles in the wort act as nucleation sites for carbon dioxide bubble formation, thereby preventing the dissolved carbon dioxide concentration from rising to a level which the yeast cannot readily tolerate. On the other hand, the use of cloudy wort has been associated with problems such as cleaning difficulties and poorer beer stability. Experiments are described in which the fermentative performance of a lager yeast in clear and cloudy worts, prepared from the same grist, and in a model solution was compared. It was found that yeast performance was in fact poorer in the cloudy wort, with reduced growth, slower attenuation, higher residual free amino nitrogen at the end of fermentation and poorer beer quality, even when the wort was well aerated and a carbon dioxide nucleation stimulant was added. The flavour of the freshly finished beer was unaffected, but flavour stability was reduced. The adhesion of particles from cloudy wort to the yeast cells was considered likely to be the main cause of the problems. Commercial trials following the laboratory experiments produced very similar results, confirming the benefits of clear wort for yeast performance and beer quality as well as reduced operating costs.
Keywords : brewers' yeast clarification fermentation performance turbidity wort