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Fermented Milk

	Fermented Milk - Long before microorganisms had been discovered, butter milk and sour milk were found palatable by some people in all countries, Fermented milks are prepared by allowing the normal lactic acid producing organisms present to develop, or by inoculating fresh milk with a portion of fermented milk of good quality.
During fermentation, lactic acid thickens or curdles the milk and produces the desired sour flavour. The nature of the product depends upon following factors: 1. The source of the milk (cow, buffalo, goat, sheep, etc.) 2. The temperature to which milk is heated before inoculation. 3. The kinds of microorganisms in the starter. 4. The incubation temperature.
The market milk contains numerous species of microorganisms in varying numbers. Their activity is uncontrolled and, therefore, uniformity of product is difficult to achieve. It is often necessary and desirable to carry out controlled fermentation with specific organisms. These specific organisms have been identified. This has led to the selection and propagation of known cultures, sometimes referred to as starter cultures. The principal organisms employed are species of Streptococcus, Leuconostoc and Lactobacillus.
The starter culture may be a pure culture or mixture of known organisms. Each product requires its own special starter and these contain different mixtures of organisms.The starter must be capable of producing lactic acid at a rapid rate and outgrowing undesirable contaminants. Even where only a single species is present in the starter, it is customary to use several different varieties of the same species. This gives protection against culture being destroyed by a specific bacteriophage. For these purposes lyophilized or other pure, stock cultures of desired organisms are maintained by several commercial laboratories.
	The consumption of fermented milk preparations is widespread because of their supposedly therapeutic value. Metchnikoff (1908) developed the idea that the usual Coliform and Clostridial bacteria in the intestine of man form putrefactive products which are distinctly injurious and the cause of definite symptoms of disease. He even expressed the opinion that these products are a common cause of death attributed to old age. The remedy he advocated was to prevent the activity of these putrefiers by acidifying the intestinal contents with lactic acid.

This might be done by drinking fermented milk and introducing Lactobacillus bulgaricus which he had isolated from Bulgarian fermented milk. This would prevent decomposition of proteins and thus one might live for long periods as was the case with Bulgarian people.

It was found later that L. bulgaricus does not survive for very long in the intestine but L. acidophilus does and it also makes an excellent tasting fermented milk.

In recent years antibiotics are widely used which disturb the normal balance of bacteria in the intestine. This has given a new impetus to the practice of consuming Lactobacilli. This ensures the establishment of desirable microflora in the intestine during or after antibiotic treatment.

Fermented milks appear under various names. The names identify the country or region where they are produced and do not necessarily mean that they are fermented with different organisms. Some preparations contain only one organism while others result from the combined action of two or more organisms.

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