Fermentation

Fermentation is a group of chemical reactions induced by microorganisms or enzymes that split complex organic compounds into relatively simple substances. Examples include the anaerobic conversion of sugar to carbon dioxide and alcohol by yeast, or bacteria converting carbohydrates into a lactic acid.

History
There were many microbiologists and other scientists that argued on the process of fermentation. However, French chemist Louis Pasteur encountered information that brought an end to the arguments. Through a variety of investigations, during the 1850s and 1860s, he concluded that fermentation was initiated by living organisms. In 1857, Louis Pasteur demonstrated that living organisms cause lactic acid fermentation. But through other scientist carefully evaluating his observations, they realized he wasn't completely correct. Scientists, including Pasteur, attempted to extract the fermentation enzyme from yeast, but the outcome was unsuccessful. In 1897 success came through, when German chemist Eduard Buechner got some yeast and extracted juice from it. He then realized that the "dead" liquid would be able to ferment a sugar solution and that solution would form a carbon dioxide and alcohol, just like a "living" yeast. It was then finally understood that fermentation was caused by enzymes produced by microorganisms. In 1907, Eduard Buechner won a Nobel Prize in chemistry for his work, and because of that, a new era in enzyme and fermentation studies was opened.

Types of fermentation
Solid State Fermentation

In this fermentation, microbial growth and formation take place at the surfaces of the solid substrates. Examples of this kind of fermentation are mushroom cultivation, starter cultures, and mold-ripened cheeses. This concept has been recently used in the production of extracellular enzymes, certain valuable chemicals, fungal toxins, and fungal spores. Several agricultural products, e.g., rice, wheat, maize, soybean, etc., are traditional substrates. Based on their physical state, solid state fermentations are split into two groups: A) low moisture solids fermented without or with occasional/continuous agitation, and B) suspended solids fermented in packed columns through which liquid is circulated. The fungi that is used for solid state fermentations are mostly likely obligate aerobes.This type of fermentation on a large scale use stationary or rotary trays. Circulating throughout the stacked solids is temperature and humidity controlled air. A less frequently used fermenter is a rotary drum type. Solid state fermentation has unique advantages, but suffers from important disadvantages.Nevertheless, commercial use of this process for biochemical production is chiefly confined to Japan.

Anaerobic Fermentation

For this type of fermentation, air is not usually needed. There are certain situations that may require air; for example inoculum build up. In the headspace of the fermenter the present air needs to be replaced with CO2, H2, N2, or a combination of these. That is something important, specifically for obligate anaerobes; Clostridium. During the process of the fermentation CO2 and H2 are usually released and then collected.

Aerobic Fermentation

An adequate amount of air is the main objective in aerobic fermentation. In specific cases, the amount of air that is required per hour is around 60 times the medium volume. The bioreactors used in this type of fermentation need an appropriate amount of sterile air and are either closed or batch types. These fermenters have a mechanism used for mixing and stirring of the medium and cells.

Uses
Alcohol

The types of alcoholic beverages that can be created by fermentation vary widely. It depends on two factors: the plant that is being fermented and the enzymes being used in the fermentation process. Many people use berries, grapes, corn, rice, wheat, honey, potatoes, barley, hops, cactus juice, cassava roots, and other kinds of plant materials. Fermentation of barley, hops, and/or malt sugar produce beer.

Early in history, many people would use naturally occurring yeast for the fermentation they needed. Today, wine-makers have the capability of selecting from a variety of specifically cultured yeast that control the exact direction the fermentation decides to take.

A very successful production is that of ethyl alcohol. The carbon dioxide that is produced when being fermented is also a key factor in the making of many baked goods. For example, when making the batter for the bread, the person may mix in a small amount of sugar and yeast/ Once the rising period takes place, sugar is fermented by the enzymes in the yeast, with the formation of the carbon dioxide gas. The carbon dioxide added gives the batter a specific bulkiness and texture that would not be there without the fermentation process. The production of ethyl alcohol is especially successful for the use in gasohol. Gasohol is a combination of around 90% gasoline and 10% alcohol. The alcohol required for gasohol can be gathered from the fermentation of agricultural and municipal wastes. Using gasohol gives a promising method for using renewable resources, plant material, for the extension of the availability of nonrenewable resource, gasoline.

Fermentation is also used in the process of treatment of waste water. During the activated sludge process, aerobic bacteria is used to ferment the organic material that is in the waste water. Solid waste is converted to carbon dioxide, water, and mineral salts.

Food Preparation

Many different types of bacteria are used in the production of cucumber pickles, sauerkraut from raw olives, cucumbers, cabbage, and olives. The selection, for example acidity and salt concentrations, of the precisely right bacteria and right conditions is a talent during producing food with the flavors wanted by the maker.

Video
A simple demonstration on the fermentation of sucrose and flour by yeast. wL-hEvZuPAU