VIEW ARTICLE    DOI: 10.1094/ASBCJ-60-0135

Fermentation Characteristics of Dried Brewers Yeast: Effect of Drying on Flocculation and Fermentation (1). D. A. Finn (2) and G. G. Stewart, International Centre for Brewing and Distilling, Biological Sciences, Heriot-Watt University, Riccarton, Edinburgh, EH14 4AS, United Kingdom. (1) Some of the results reported in this paper were presented at the 66th Annual ASBC meeting held in Victoria, British Columbia, Canada. (2) Corresponding author. Phone: +131 4495111; Fax. +44 131 4497459; E-mail: <d.a.finn@hw.ac.uk> J. Am. Soc. Brew. Chem. 60(3):135-139, 2002. Accepted May 13, 2002.

Strains of freshly propagated ale and lager yeast were compared with identical dried strains during wort fermentations. While several factors remained within standard expectations and were favorably matched to freshly propagated yeast fermentation results, a number of undesirable characteristics were associated with the dried yeast brews, especially reduced viability. The Helm flocculation test and static fermentations showed that flocculation is affected by the drying process, especially with lager strains. Also, dried yeast seems to induce a greater amount of haze in suspension, and the fermentation has a considerably less stable foam than fermentations with the fresh yeast samples, which may be due to the increased levels of extracellular proteinase found. It is suggested that many of the effects observed are a result of pitching high levels of dead yeast into the wort and that this could be alleviated by increasing the viability of the dried yeast, possibly by propagating on carbon sources such as maltose to increase levels of trehalose, a reported stress protectant. Keywords: Cell wall, Haze, Proteinase, Trehalose

Cepas de levadura de ale y lager recién propagadas fueron comparadas con cepas idénticas secas durante la fermentación de mosto. Mientras varios factores permanecian entre expectativas estándares y sé comparaban favorable con los resultados de levadura recién propagada, una enumerada cantidad de características indeseables se asociaron con las cervezas de levadura seca, especialmente con la reducción de viabilidad. Las pruebas de floculación Helm y fermentaciones estáticas demostraron que la floculación es afectada por el proceso de secado, especialmente con las cepas lager. La levadura seca también parece provocar una mayor cantidad de calina en suspensión, y la fermentación tiene una espuma menos estable que las muestras de fermentaciones con levadura fresca, cuál puede ser debido a los niveles elevados encontrados de proteinasa extracelular. Se sugiere que muchos de los efectos observados son los resultados de altos niveles de inoculación de levadura muerta en el mosto y que esto se puede aliviar con incrementar la viabilidad de la levadura seca, posiblemente con la propagación en fuentes de carbón como maltosa para incrementar los niveles de trehalose, un reportado protector de stress. Palabras claves: Calina, Pared de célula, Proteinasa, Trehalose