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Low-Carbohydrate Beer Production: Issues with Sticky Yeast Beds

MBAA TQ vol. 44, no. 2, 2007, pp. 108-115  |  VIEW ARTICLE

Eric J. Samp (1), Larry Silberman (2), and Leah Dennison (1). 1. Coors Brewing Company, MS BC600, Golden, CO 80401. 2. Gusmer Enterprises, Inc., 81 M St., Fresno, CA 93721.

Abstract
During the production of low-carbohydrate beers (LCB), ergonomic problems arose when harvesting lager yeast from our horizontal box fermenters. Yeast pushers had an extremely hard time when pushing the yeast out of the tank bottom because the yeast beds would set up into a thick, sticky slurry. Initial attempts to understand the mechanism of the sticky yeast in our LCB fermentations by applying common theories on yeast flocculation were unsuccessful. We then theorized that an uncommon flocculation mechanism might be implicated in trub binding to yeast cells, causing their electro-kinetic properties to change during the course of fermentation. We discovered that commercial glucoamylases employed in mashing for LCB production hindered hot-break formation in our whirlpool vessels, leading to higher levels of trub carryover into the fermenters. After measuring the zeta potential of both the trub and the yeast over various pH levels typically observed in these fermentations, we speculated that an electrostatic interaction occurred between the negatively charged yeast cells and the positively charged trub proteins once the beer pH dropped below a certain threshold. This difference in charge could have caused the sticky yeast observed only in our LCB fermentations. To examine this hypothesis, tests were conducted to control pH drop during fermentation while observing the characteristics of the yeast bed. By controlling yeast growth during fermentation and subsequently keeping the beer pH above 4.0, we were successful in alleviating the sticky yeast bed phenomenon.

Keywords: glucoamylase effects on trub formation, sticky yeast, �trubid� wort, zeta potential

 

S�ntesis
Se experimentaron problemas ergon�micos al cosechar la levadura de nuestros fermentadores horizontales durante la producci�n de cervezas de bajo contenido de carbohidratos (LCB). Los empujadores de levadura tuvieron muchas dificultades al tratar de sacar la levadura del fondo debido a que los sedimentos de levadura resultaban muy gruesos y pegajosos. No se pudo llegar a ninguna explicaci�n del mecanismo de formaci�n de esta levadura pegajosa aplicando teor�as comunes de floculaci�n de levadura. Posteriormente se consider� que podr�a estar implicado un mecanismo inusual de floculaci�n, donde el trub se adhiere a la levadura ocasionando un cambio en sus propiedades electrokin�ticos en el curso de la fermentaci�n. Descubrimos que glucoamilasas comerciales empleadas en la maceraci�n para la producci�n de LCB dificult� la formaci�n de trub caliente en nuestros tanques whirlpool, ocasionando una mayor cantidad de trub a los fermentadores. Se midi� el potencial zeta tanto del trub y de la levadura a diferentes niveles de pH, lo que nos llev� a especular que ocurr�a una interacci�n electrost�tica entre las c�lulas de levadura (con carga negativa) y la prote�na del trub (con carga positiva) al bajar el nivel del pH en el fermentador por debajo de un umbral. La diferencia en las cargas est�ticas pudo haber causado la levadura pegajosa encontrada �nicamente en los fermentadores con LCB. Se test� la hip�tesis con pruebas donde se control� la ca�da del pH durante la fermentaci�n a la vez de observar las caracter�sticas del sedimento de levadura. Pudimos aliviar este problema mediante el control de la reproducci�n de levadura durante la fermentaci�n y manteniendo el pH de la cerveza por encima de 4.0.

Palabras claves: efecto de glucoamilasa sobre la formaci�n de trub, levadura pegajosa, mosto turbio, potencial zeta

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