Studies on the Uptake and Metabolism of Wort Sugars During
Brewing Fermentations
MBAA TQ vol. 43, no. 4, 2006, pp.
265-269 |
VIEW ARTICLE
G. G. Stewart. The International Centre for Brewing
and Distilling (ICBD), Heriot-Watt University, Riccarton, Edinburgh
EH14 4AS, United Kingdom.
Abstract
Brewers� wort contains five fermentable sugars: glucose, fructose,
sucrose, maltose, and maltotriose. In most worts, maltose is the highest
concentration, followed by maltotriose and glucose. These sugars are taken
up by yeast in a distinct order (or priority), with glucose repressing the
uptake of maltose and maltotriose. Glucose is taken up without the
expenditure of yeast metabolic energy, whereas maltose and maltotriose
uptake requires energy (active transport). The concentration of each
sugar, together with their relative proportions to one another, influence
overall wort fermentation rate and extent. There are also differences
between ale and lager yeast strains with respect to wort sugar uptake
characteristics. For example, ale strains are less able to utilize wort
maltotriose than lager strains. In addition, the concentration of wort
glucose and maltose influence beer flavor. In particular, wort with
elevated levels of glucose produces beers with high concentrations of
esters (particularly ethyl acetate and isoamyl acetate). Worts containing
high levels of maltose, however, produce beers with much reduced
concentrations of these esters. This is particularly the case with
high-gravity worts (>16�Plato).
Keywords: esters, glucose, high-gravity wort, maltose, maltotriose,
osmotic pressure, yeast viability, yeast vitality
S�ntesis
El mosto cervecero contiene cinco az�cares fermentables: glucosa,
fructosa, sacarosa, maltosa, y maltotriosa. En la mayor�a de los mostos,
maltosa tiene la mayor concentraci�n, seguido por maltotriosa y glucosa.
Estos az�cares son transformados por la levadura en una orden (o
priori�dad) muy espec�fico, con glucosa represando el consumo de maltosa y
maltotriosa. La glucosa es absorbida sin gastar energ�a metab�lica de la
levadura, mientras que la absorci�n de maltosa y maltotriosa requiere
energ�a (transporte activo). La concentraci�n de cada az�car, junto con la
proporci�n relativa de uno con los otros, afecta la velocidad de la
fermentaci�n y la cantidad total fermentada. Tambi�n existen diferencias
entre especies de levadura de alta y baja fermentaci�n con respecto a su
absorci�n de diferentes az�cares. Por ejemplo, levaduras de alta
fermentaci�n son menos capaces de utilizar maltotriosa del mosto que
levaduras de baja fermentaci�n. Vale notar que la concentraci�n de glucosa
y maltosa en el mosto influye sobre el sabor de la cerveza final; mostos
con altos niveles de glucosa producen cervezas con altas concentraciones
de esteres (especialmente acetato de etilo y acetato isoam�lico). Mostos
que contienen altos niveles de maltosa producen cervezas con una mucha
menor concentraci�n de estos esteres. Esto es particularmente verdad para
el caso de mostos �high-gravity� (>16�Plato).
Palabras claves:
esteres, glucosa, mosto �high-gravity�, maltosa, maltotriosa, presi�n
osm�tica, viabilidad de levadura, vitalidad de levadura
