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The complexity of yeast extracts and its consequences on the utility in brewing: A review
F. F. Jacob, M. Michel, M. Zarnkow, M. Hutzler and F.-J. Methner

From an international perspective, one particular approach to increase the profitability of the modern industrial brewing process is to ferment high-gravity worts with high proportions of unmalted grain. However, the nutrients provided for yeast in these methods are often insufficient to achieve a satisfactory fermentation result and product quality. Yeast extracts, referred to as "yeast foods", can optimize these fermentation processes because they provide a multitude of essential nutrients for the fermenting yeast such as free alpha-amino nitrogen, minerals and vitamins, or generate an added benefit for a product as a result of their antioxidative properties. In industrial manufacturing processes of yeast extracts, which take advantage of autolytic, hydrolytic, plasmolytic, thermal and mechanical methods, this nutrient composition can be controlled through the choice of process parameters and the used yeast quality. As a consequence, the complex yeast extract composition made from bioactive components varies greatly in commercially available products and can thereby influence fermentation in different ways. In beer production, the high number of physiologically effective yeast extract components stimulates the yeast's fermentation performance in various ways, depending on the oxygen supply and wort composition. Besides enhanced fermentation rates, individual nutrients of the yeast extract also influence the yeast secondary metabolism and thereby the overall flavor of the beer. Based on the specified complex interrelationships, this review intends to first provide an overview of the different bioactive substances of a yeast extract and explain the technical manufacturing background. It then discusses the physiologically effective components of the yeast extract when used in the brewing process. Various results of individual papers will also be examined for production-related nutrient variations.

Descriptors: yeast extract, brewer's yeast, autolysis, mechanical disruption, high gravity, fermentation performance

BrewingScience, 72 (March/April 2019), pp. 50-62