Fermentation

From Freepedia

In its strictest sense, fermentation (formerly called zymnosis) is the anaerobic metabolic breakdown of a nutrient molecule, such as glucose, without net oxidation. Fermentation does not directly produce energy in cells; it merely allows glycolysis (a process that yeilds two ATP per glucose) to continue. Fermentation yields lactate, acetic acid, ethanol, or some other simple product.

Fermentation is also used much more broadly to refer to the bulk growth of microorganisms on a growth medium. No distinction is made between aerobic and anaerobic metabolism when the word is used in this sense.

This process is often used to produce or preserve food. Fermentation typically refers to the fermentation of sugar to alcohol using yeast, but other fermentation processes include the making of yogurt. The science of fermentation is known as zymology.

Fermentation usually implies that the action of the microoganisms is desirable. Occasionally wines are enhanced through the process of cofermentation.

Contents

Uses

The primary benefit of fermentation is the conversion, e.g. converting juice into wine, grains into beer, and carbohydrates into carbon dioxide to leaven bread.

According to Steinkraus (1995), traditionally food fermentation serves five main purposes:

  1. "Enrichment of the diet through development of a diversity of flavors, aromas, and textures in food substrates"
  2. "Preservation of substantial amounts of food through lactic acid, alcoholic, acetic acid, and alkaline fermentations"
  3. "Enrichment of food substrates biologically with protein, essential amino acids, essential fatty acids, and vitamins"
  4. "Detoxification during food fermentation processing"
  5. "A decrease in cooking times and fuel requirements"

Fermentation has some benefits exclusive to foods. Fermentation can produce important nutrients or eliminate antinutrients. Food can be preserved by fermentation, since fermentation uses up food energy and can make conditions unsuitable for undesirable microorganisms. For example, in pickling the acid produced by the dominant bacteria inhibit the growth of all other microorganisms.

In alchemy, fermentation is often the same as putrefaction, meaning to allow the substance to naturally rot or decompose.

Fermented foods, by region

History

Since fruits ferment naturally, fermentation precedes human history. However, humans began to take control of the fermentation process at some point. There is strong evidence that people were fermenting beverages in Babylon circa 5000 BCE, ancient Egypt circa 3000 BCE, pre-Hispanic Mexico circa 2000 BCE, and Sudan circa 1500 BCE. There is also evidence of leavened bread in ancient Egypt circa 1500 BCE and of milk fermentation in Babylon circa 3000 BCE. The Chinese were probably the first to develop vegetable fermentation.

Products

Yeast produce ethanol and carbon dioxide gas. When the ferment has a high concentration of pectin minute quantities of methanol can be produced. Usually only one of the products is desired; in bread the alcohol is baked out, and in alcohol production the carbon dioxide is released into the atmosphere.

Products produced by fermentation, such as ethanol and lactic acid, are used as a substitute for oxygen. During cellular respiration, oxygen is the final electron acceptor. However, when no oxygen is available, ethanol and lactic acid are used in place of oxygen.

Depending on the type of fermentation, some products (eg: fusel alcohol) are harmful to people's health.

Bacteria generally produce acids. Vinegar (acetic acid) is the direct result of bacterial fermentation. In milk, the acid coagulates the casein, producing curds. In pickling, the acid preserves the food from pathogenic and putrefactive bacteria.

See also

References

  • Steinkraus, K. H., Ed. (1995). Handbook of Indigenous Fermented Foods. New York, Marcel Dekker, Inc.
  • The 1811 Household Cyclopedia
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