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Understanding The Fermentation Process

The world, as we know it, is continued by a process of creation and decay. Without decay the accumulation of dead organic matter of all kinds, would so clutter the earth that life itself would be stifled. This decay is caused by micro-organisms that break down the debris to elements that will sustain further life as it is created. One stage of decay - a stage that is only one of a cycle in the overall process - is fermentation which causes effervescence, heat and a change of properties.

The creation of wines and beers is caused by fermentation. It is the action of yeast which decays, or breaks down, the sugars in vegetable matter. This fermentation of sugar is but one stage in converting vegetable matter which contains sugar (eg fruit) from its complete form to chemicals and compost. After the yeast has reduced the sugar to alcohol and carbon dioxide, other yeasts and bacteria cause further fermentation that ultimately reduces the wine to carbon dioxide and water.

This full process has only been understood in recent years, and better control of the production of wine and the prevention of spoilage during and after its production has resulted.

The sucrose which is present in a must, either from the raw materials, or from the addition of sugar, is hydrolysed into simple sugars by the enzyme called invertase, secreted by the saccharomyces yeast.

The yeast also secretes a complex of enzymes, called zymase, which causes the glucose and fructose to change into carbon dioxide and ethyl alcohol whilst releasing energy. The escaping carbon dioxide gas produces the effervescence which is called the visible signs of fermentation. The ethyl alcohol is the basic part of wine, and the large calories of energy are utilised by the yeast. Maltose, used in the brewing of beers, is hydrolysed and fermented in a similar manner. The difference is an enzyme called maltase which hydrolyses the maltose to glucose only. The glucose is then fermented by the enzyme complex as described above.

It was generally believed at one time that to exist all forms of life required oxygen as an energy source. It was believed that in a covered must the yeast obtained oxygen from sugar as a result of fermentation. It is now certain, that wine yeasts do not require oxygen as an energy source. The energy they require is that released by the fermentation and they take no oxygen.

Otto Myerhoff conclusively proved in 1948 that yeast only required oxygen for reproduction; it can live without oxygen but will not reproduce itself. This oxygen is obtained from the air or from the oxygen dissolved in a solution. Thus the sole purpose of fermentation, as far as the yeast is concerned, is to provide itself with energy not oxygen.

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