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