Polysaccharides are large complex molecules containing 3 or more monosaccharides (and in some cases number more than several thousand simple sugar molecules) which are used by living organisms to store energy. They also form part of cell structural fibres. Starch consists of many glucose monosaccharides hooked together in both linear and branched forms. Pectin, gums, and cellulose are some of the other main polysaccharide molecules. Unfortunately cellulose is normally only fermented by xylose fermenting yeasts or bacteria so at least 30% of any plant materialis is generally always unfermentable. For polysaccharides to be fermentable they need to be split or broken down (hydrolyzed) again into simple sugars. This can be acheived by enzymes, acids, or heat.

Quite often the process is a joint one combining two or all three of these. The main enzymes used or part of alcohol fermentation are Alpha amylase, Beta amylase, Glucamylase (Amylogglucosidase), all of which are used to break down amylose (major component of starch) and amylopectrin (other major component of starch which is less easily hydrolyzed due to its large branched chains nature of construction). In addition other enzymes that are used are Beta glucanase, Lactase (milk sugar enzyme), Maltase, and Protease. Zymase is the complex of enzymes produced by yeasts which are responsibler for the fermantation of sugars to ethanol.

Acids that are involved or used in fermentation are Tartaric, Malic (wine), Succinic, Lactic, Citric, Proprionic, Sulpheric, and Hydrochloric.

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