Fermentation

Fermentation is a chemical process that breaks down carbohydrates and other organic materials and produces energy without using oxygen. This process is carried out by microorganisms such as bacteria, molds, and fungi. Alcohol fermentation is a well-known type of fermentation where sugar is broken down into alcohol and carbon dioxide.

LOUIS PASTEUR

One of the most extraordinary scientists in history, French chemist and microbiologist (a person specializing in the study of microorganisms) Louis Pasteur (1822–1895) is considered the founder of microbiology. He also contributed to our understanding of fermentation (a chemical process that breaks down carbohydrates and other organic materials and produces energy without using oxygen), developed the germ theory of disease, improved immunization, and proved that heating kills microorganisms (an organism of microscopic size). This process of using heat was named pasteurization after the famed scientist.

Louis Pasteur was born in Dole, France, and his family moved to Arbois when he was very young. He attended school there and appeared to be a mediocre student in every way. Still, he stayed in school despite near poverty, and after attending a lecture in chemistry and being inspired by it, he decided to study this new and fascinating subject. Studying chemistry, he suddenly became an excellent student, and by the age of twenty-six earned his Ph.D. and made a major discovery concerning crystals for which he won a national award.

By 1854, the "mediocre" student had become dean of the Faculty of Sciences at the University of Lille, and was asked by the French wine industry to help them with their spoilage problem. Very often, wine and beer spoiled, or went sour, as they aged, ruining tons of good beverage without anyone knowing why or what to do. Pasteur took up the problem and discovered almost immediately with his microscope that the yeast (various single-celled fungi capable of fermenting carbohydrates) in sour wine had an elongated shape, while the yeast in good wine was spherical, or round. When the good (round) yeast ferments, it produces alcohol. When the bad (elongated) yeast ferments, it produces lactic acid (a syrupy liquid). He suggested heating the wine or beer gently at about 120°F (48.9°C) after it had been properly made. Pasteur stated that the heat would kill any yeast left, especially the bad yeast, and if the wine were properly corked, it would not go sour. Heating wine seemed barbaric to the French, but they tried the experiment and it worked. Ever since, a gentle heating that kills unwanted microorganisms has been called pasteurization. Besides beer and wine, milk also is now pasteurized.

Saving the French wine industry made Pasteur a hero, so it is not surprising that its silk industry asked him to do the same thing for them. He did by showing them how to get rid of a killer parasite (an often harmful organism that lives on or in a different organism) that was killing the silk worms. This led Pasteur to work with communicable (contagious) diseases. He had long felt that disease was something that was caused by unseeable organisms and then was spread person-to-person. By now, Pasteur had considerable experience using his microscope to identify different kinds of microorganisms such as bacteria and fungi. So when he decided to work on what is now called the germ theory of disease, he was following one of his favorite sayings, "Chance favors the prepared mind." Pasteur then developed techniques for culturing (growing) and examining several disease-causing bacteria. He identified both Staphylococcus and Streptococcus, which cause serious, sometimes fatal infections, and also cultured the bacteria that cause cholera. It was in working with these infectious bacteria that Pasteur realized that weakening them allows them to be used as a vaccine. From this discovery, he developed a vaccine for the disease anthrax, as well as one for rabies, a deadly disease contracted from the bite of an infected, rabid animal. If any individual had achieved one or two of these accomplishments, he or she would be considered among the pioneers in the life sciences. Yet Pasteur did all this and more. His germ theory of disease is considered by many scientists as the single most important medical discovery of all time because it not only showed doctors how to fight and prevent disease, but it supplied the all-important correct theory that would guide future research. Pasteur is truly one of the giants of biology.

Fermented products have been used by people for thousands of years, primarily to make the alcohol in beer and wine and to make bread dough rise. Although they did not understand what made it happen, the ancient Egyptians knew that if they allowed bread dough to stand for several hours, it became lighter and better tasting than if baked immediately. What they did not know was that the dough was lightened by the carbon dioxide gas produced by the fermentation of sugar. This happened not because the Egyptians knew enough to add yeast (a single-celled fungus) to the dough, but because leaving the dough uncovered allowed microscopic organisms like yeast and bacteria to float in on the breeze and break down the dough's sugars into alcohol and carbon dioxide. The carbon dioxide gas then became trapped in the dough and made it rise, while the alcohol would evaporate during baking. The Egyptians also discovered that by allowing certain grains like barley to begin to spoil, they could obtain a drink with a pleasing side effect (alcohol). The same effect could be achieved by allowing grapes to spoil since grapes contain yeast that grow naturally on their skins.

Throughout history, the process of fermentation was shrouded in mystery and superstition. During the seventeenth century, the English chemist Robert Boyle (1627–1691) correctly predicted that an understanding of the fermentation process would lead to the discovery of the causes of other phenomena like disease. Boyle's prediction came true when the French chemist, Louis Pasteur (1822–1895), proved that yeast caused fermentation in beer and wine. After this discovery, Pasteur turned his research toward the spread of diseases caused by other microorganisms.

Pasteur's work saved France's wine industry, which could not understand why its burgundy wine was spoiling. Pasteur discovered that wine normally contained yeast cells that produced alcohol. However, he also realized that wine containing bacteria and other microorganisms produced lactic acid when they fermented, and thus spoiled the wine. Pasteur showed that fermentation caused by living organisms is too small to be seen without a microscope, and that the end product of the fermentation process depends on both what is being fermented and what microbes are the catalyst (something that starts a chemical reaction). Pasteur taught France's wine industry how to kill unwanted bacteria by the gentle heating of the wine at about 120°F (48.9°C). This process is called pasteurization after the great scientist.

Today, fermentation is well understood and can be controlled. Fermentation is a large part of today's food industry, with some form of fermentation taking place in the production of many food products like yogurt, buttermilk, cheese, soy sauce, cured meats, pickled vegetables, and chocolate, as well as in alcoholic beverages and bread. In some cases, antibiotics and other medications can be produced by fermentation, as can ethyl alcohol that is added to gasoline to produce gasohol. Fermentation is also critical to today's disposal of solid waste by converting it to carbon dioxide, water, and mineral salts.

[See alsoBacteria; Carbohydrates; Carbon Dioxide; Fungi ]