The Control of Ester Synthesis During Wort Fermentation

Graham Stewart, Amanda Lyness and Imar Younis. Presented at the MBAA 111th Anniversary Convention, Minneapolis, Minnesota, September, 1998.

Abstract
Acetate esters are an important group of beer flavour compounds. These compounds are formed by yeast during fermentation but the mechanisms that control their production are not completely clear. Fermentation conditions which are known to affect the beer's ester level and thereby its flavour profile include temperature, fermenter geometry, yeast strain and condition and wort composition (for example, sugar spectrum and gravity). The enzyme alcohol acetyltransferase (AAT) and its corresponding gene(s), AFT, have been implicated in the synthesis of a number of acetate esters. It would appear that these are separate genes (AFT1 and AFT2) for the synthesis of ethyl acetate and isoamyl acetate. An example of wort composition influencing ester levels is the finding that high gravity worts with elevated maltose concentrations produce lower levels of acetate esters than similar gravity worts with high levels of glucose or fructose.
Keywords: ester synthesis, yeast, flavours, alcohol acetyltransferase (AAT)  

Sintesis
Esteres de acetato son un grupo importante de compuestos de sabor de la cerveza. Estos compuestos son formados por la levadura durante la fermentacion, pero los mecanismos que controlan su produccion no estan claros. Las condiciones de fermentacion que se conocen afectan el perfil de sabor de la cerveza incluyen temperatura, la geometria del fermentador, condicion de la levadura y la comosicion del mosto (por ejemplo, el espectro de azucar y gravedad original). La enzima de alcohol acetiltransferase (AAT) ha sido implicada en la sintesis de un numero de esteres de acetato pero esta sintesis no esta controlada por un factor controlador. Esta hipotesis es sustentada por la observacion de que el mosto que contiene altos niveles de glucosa o fructuosa producen altos niveles de esteres de acetato cuando son comparados al mosto que contiene altos niveles de maltosa.