Fermentation
In the absence of the gas oxygen, certain living things are capable of breaking down carbohydrates (starches and sugars) to form alcohol and carbon dioxide gas. This process is known as anaerobic respiration or fermentation, and it has been used for centuries in the production of certain foods and beverages.
Throughout history, the process of fermentation was shrouded in mystery and superstition. Many thought that the process was spontaneous, just as they believed that life arose spontaneously from nonliving things. During the seventeenth century, English chemist Robert Boyle proclaimed that an understanding of the fermentation process would lead to an understanding of the cause of other phenomena like disease. His prediction came true two centuries later. In the mid 1800s, a French scientist, Charles Cagniard de Latour, first discovered that tiny living cells called yeast can cause fermentation. This paved the way for the seminal experiments on yeast fermentation performed several years later by French scientist Louis Pasteur.
Pasteur was dedicated to analyzing what really happens during fermentation after being asked to find out why some of the greatest burgundy wine produced in France was spoiling. After observing wine under the microscope, Pasteur noted that wine normally contained yeast cells which were producing the desired alcohol but wine that had become sour contained bacteria, other microorganisms that produced lactic acid during fermentation, spoiling the wine. Pasteur's experiments showed that fermentation could take place only in the presence of living cells. His hypothesis countered the argument of a great chemist of the time, Justus von Liebig, who erroneously explained that fermentation was a chemical reaction caused by the decomposition of dead yeast cells. Pasteur's correct theory of fermentation led him to research in other related fields of microbiology which included his work on the cause and treatment of numerous diseases caused by microorganisms.
The fermentation process is caused by enzymes, catalysts in chemical reactions similar to the digestive enzymes in the human body. Certain enzymes act on starch to break down the long chain-like molecules into smaller units of sugar. Then other enzymes convert one kind of sugar molecule to another. Still other enzyme reactions break apart the sugar molecule (composed of carbon, hydrogen and oxygen) into ethyl alcohol and carbon dioxide gas.
The production of carbon dioxide and alcohol are incidental to the release of energy needed by organisms such as yeast to survive. But these metabolic by-products have been used in human enterprise for centuries. The yeast Saccharomyces cerevisiae is traditionally added to liquids derived from grains and fruits to brew beer and wine. The natural starches and sugars provide food for the yeast and during fermentation the desired alcohol is released. In China for thousands of years, traditional soy sauce or shoyu was brewed by adding the fungus Aspergillus oryzae to a mixture of boiled soybeans and wheat and allowing it to ferment for about a year.
In recent times, yeasts have been used to aid in the production of alternative energy sources. Yeasts are placed in large fermentation vats containing organic material. During fermentation the yeast convert the organic material into ethanol fuel. Researchers are working on developing yeast strains that will convert even larger organic biomasses into ethanol more efficiently.
The fermentation process is not limited to microorganisms. It takes place on occasion in animals. If goldfish are placed in anaerobic conditions they can survive for a limited time without oxygen by carrying on fermentation provided that the water is cold enough to reduce their metabolic needs. In human beings, fermentation occurs in muscle tissue during periods of exercise. When energy requirements are high during strenuous exercise, oxygen cannot be delivered fast enough. To continue supplying the muscle with energy, sugar molecules in the tissue are converted to lactic acid. However, the buildup of lactic acid causes fatigue and even after exercise ceases, breathing continues to be heavy to get more oxygen back into the tissue.
This is the complete article, containing 644 words
(approx. 2 pages at 300 words per page).
