Making Sense of Flavor Change in Beer

PEER REVIEWED SUBMISSION

By Charles W. Bamforth Department of Food Science and Technology, University of California, Davis, California. This paper was originally presented at the MBAA 112th Anniversary Convention, Keystone, Colorado, 1999.

Abstract
By critical evaluation of published literature and the application of reasoning based on the laws of chemistry and physics, the potential for addressing staling in beer has been assessed. The key factors that determine the flavor life of beer are oxygen content of the packaged product, the level of sulfur dioxide in the beer and the temperature encountered by the beer in storage. It is argued that upstream oxida-tion, while not unimportant, has perhaps been overplayed. It is impor-tant, however, that yeast has the opportunity to 'clean up' any upstream oxidation through its ability to reduce carbonyl species. Adducts between carbonyls and sulfur dioxide are not reduced by yeast, and therefore it seems that the preferred strategy would be one of minimizing SO₂ production by yeast, in particular as this would allow better conversion of acetaldehyde to alcohol. Acetaldehyde has a far greater binding capacity for SO₂ than have the staling aldehydes and its presence interferes with the ability of agents to bind staling substances.
Keywords: staling, oxygen, sulfur dioxide, carbonyl  

Sintesis
Mediante la evaluaci�n cr�tica de la literatura publicada y la apli-caci�n de razonamiento basado en las leyes de qu�mica y f�sica, se ha evaluado la posibilidad de dirigir el problema de echarse a perder de la cerveza. Los factores claves que determinan la vida del sabor de la cerveza son el contenido de ox�geno del producto empacado, el nivel de di�xido de azufre en la cerveza y la temperatura a la que se encuentra la cerveza durante el almacenado. Se ha discutido que la oxidaci�n a contracorriente, aunque no es sin importancia, a lo mejor ha sido sobre valuada. Es importante sin embargo, que la levadura tenga la oportunidad de limpiar cualquier oxidaci�n a contracorriente mediante su habilidad de reducir especies de carbonilos. Los aductos entre los carbonilos y el di�xido de azufre no son reducidos por la levadura y por lo tanto parece ser que la estrategia preferida ser�a la que mantuviera a un m�nimo la producci�n de di�xido de azufre por la levadura, particularmente por que esto permitir�a una mejor con-versi�n del acetaldeh�do a alcohol. El acetaldeh�do tiene una capaci-dad de uni�n mas fuerte por el di�xido de azufre que los acetaldeh�dos echados a perder y su presencia interfiere con la habil-idad de los agentes de unirse a substancias echadas a perder.