Fermentation Symposium�Part I New Developments in Ethanol Fermentation

Stewart, G.G.

Abstract
Production of ethanol by microorganisms, as a result of the fermentation of substrates such as sugars or starch, is a process that predates recorded history. Although a number of microorganisms are able to produce ethanol, more than 96% of the fermentation ethanol that is produced today employs the yeast Saccharomyces cerevisiae or its related species. Such yeast strains must be able to ferment a wide range of sugars, and yeast strains possessing amylolytic ability are becoming important as producers of fermentation ethanol from starch/dextrin-containing substrates such as wort. A brewing yeast strain must effectively remove the desired nutrients from the growth medium (i.e., the wort), must impart the required flavor to the beer, and must be effectively removed from the fermented wort after the cultures have fulfilled their metabolic role. In the normal situation, brewer�s yeast strains are incapable of fermenting dextrin material; however, yeast strains are now available that are capable of fermenting at least a part of this dextrin material and producing a palatable beer. A process is described that produces a low carbohydrate beer employing amylolytic enzymes of a derepressed Schwanniomyces castellii strain able to overproduce alpha-amylase and glucoamylase with debranching ability.