Role of Yeast in Production of Alcoholic Beverages


Microscopic image of Mackeson Triple Stout at work, courtesy micro.magnet.fsu.edu

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Introduction

Although there is a distinction between beer, wine and liquor as well as other lesser known alcoholic beverages, they share one thing in common. They are the fermentation products of yeasts, mostly Saccharomyces cerevisiae or in the case of beers, usually S. carlsburgiensis. Yeasts, as you recall, are not mycelial. They are unicellular fungi that reproduce asexually by budding or fission. The reaction by which alcoholic beverages are produced is generally referred to as fermentation and may be summarized as:

Yeast + Glucose è Alcohol (Ethanol) + CO2

This reaction is also important in baking bread, but the desired product is then the carbon dioxide rather than alcohol. The production of alcohol occurs best in the absence of oxygen. However, from the yeast’s point of view, alcohol and carbon dioxide are waste products, and as the yeast continues to grow and metabolize in the sugar solution, the accumulation of alcohol will become toxic when it reaches a concentration between 14-18%, thereby killing the yeast cells. This is the reason why the percentage of alcohol in wine and beer can only be approximately 16%. In order to produce beverages (liquor) with higher concentrations of alcohol, the fermented products must be distilled.

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