What is Yogurt?

Yogurt is a food produced by bacterial fermentation of milk.  The bacteria used to make yogurt are known as "yogurt cultures".  Fermentation of lactose by these bacteria produces lactic acid, which acts on milk protein to give yogurt its texture and its characteristic tang.


  • Worldwide, cow's milk, the protein of which is mainly casein, is most commonly used to make yogurt.


  • Milk from buffalo, goats, ewes, mares, camels, and yaks, however, is also used to produce yogurt in various parts of the world.


  • Dairy yogurt is produced using a culture of ''Lactobacillus delbrueckii subsp. bulgaricus'' and ''Streptococcus thermophilus bacteria''.


In addition, other lactobacilli and bifidobacteria are also sometimes added during or after culturing yogurt.  Some countries require yogurt to contain a certain amount of colony-forming units of microorganisms.


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A Very Short History of Yogurt

One theory of the discovery of yogurt is that early man stored the milk in the intestines of animals.  The enzymes that were present in the intestines may have started the initial fermentation process.  The early man enjoyed it and continued making it. Another thought is that early man noticed when slaughtering animals that the milk they consumed changed its form once ingested and set out to create the fermented milk intentionally.  Whatever the true story behind its discovery, yogurt spread from Central Asia to the Middle East and Europe and throughout the world.


Yogurt appears in many ancient texts including the ancient Indian Ayurvedic scripts, the Bible and historical texts by Pliny, Herodotus, Homer, and Galen.  In Genesis 18:8, Abraham may have served yogurt and milk to his guests.


The great Mongol warrior Genghis Khan is said to have encouraged the drinking of a fermented horse milk yogurt called kumis.  Mongols of all levels of the society consumed the beverage, but it was of particular importance to the warriors.  The warriors would take their horse herds with them as they travelled the steppes and always have a supply of kumis.  Genghis Khan reputedly believed that not only did the kumis keep his warriors healthy, but actually made them braver when facing their enemies.


The historical record shows that in the 16th century a Turkish doctor saved the life of King Francis I by treating him with yogurt made from goat's milk.  The king had been suffering from some type of intestinal illness that no other medicine seemed to help but was apparently cured by yogurt. This wondrous cure brought a new surge in the popularity of yogurt as a health food, though no one quite knew how the yogurt worked.


History of Bulgarian Yogurt

In return to the Prof. Massol’s letter, Prof. Mechnikov sent immediately an invitation to Stamen Grigoroff to visit The Institute Pasteur. In the big lecture hall there, Stamen Grigoroff reported the discovery of the lactobacilli. For scientific demonstration, he brought with him Bulgarian yoghurt and a microscope. The direction of Pasteur Institute entrusted Prof. Mechnikov with the task to confirm independently the discovery of Stamen Grigoroff and to report the results to the Scientific Council of the institute. Three years later this resulted in a scientific publication: “Some notes regarding the yoghurt” printed in Les Comptes rendus de l'Academie des Sciences, 1908. Soon afterwards Coendi, Mikelson, Luerson and Koen Mechnikov’s scientific assistants, named the microorganism discovered by Stamen Grigoroff Bacillus bulgaricus, “Bulgarian milk bacterium”.


Mechnikov explained the exaggerated life longevity of Bulgarians with the beneficial health effects of Bulgarian yoghurt.

Nowadays under the designation “Bulgarian yoghurt” one understands fermented milk products, obtained as a result of the activity of symbiotic culture of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus. The lactic acid fermentation, caused by those two bacterial species, induces profound changes in the milk content. The fermentation products exhibit positive health effects on the human organism. Scientific investigations demonstrated that yoghurt consumption influences positively the balance of the microbial population in the human intestine. It facilitates the assimilation of lactose, stimulates the immune system and has an anticancer effect. Metabolites produced by Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus during the fermentation process lead to increasing of the cell counts of healthy and beneficial intestinal microorganisms.

Stamen Grigorov /in the middle/ as a student in Geneve, Sweetzearland.

As an Major from Bulgarian Army Medical Corps during the IWW.

There are no exact data for the origin of Bulgarian yoghurt, but it is widely accepted that it has been derived from the Thracian tribes 4000 years B.C. The ancient Thracians observed that the fermented milk exhibits better endurance compared to the fresh milk. They obtained the product known as “sour milk” by addition of fermented milk in boiled fresh milk. By means of systematical and continuous preparation of “sour milk”, bacterial strains of two species - Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus – have been gradually selected in the Bulgarian yoghurt.Initially, the qualities of Bulgarian yoghurt were scientifically studied by the Russian biologist Ilya Mechnikov. He considered that the activity of putrefactive microorganisms in the human gastrointestinal tract might be reduced and obstructed through colonisation of the gut by lactic acid bacteria. These bacteria produce lactic acid which inhibits the growth, multiplication and development of such harmful microorganisms.

In the year 1905 Stamen Grigoroff made his famous discovery of the causative agent of the milk fermentation. His scientific advisor Prof. Massol immediately wrote a letter to Prof. Ilja Mechnikov at the Institute Pasteur, Paris:


“Persistence and tenacity in the scientific work and research are distinguishing features of my Bulgarian co-worker and assistant Stamen Grigoroff… After a number of successive experiments, he was able to discover and isolate the causative agent of Bulgarian yoghurt. Your work is inspired by the striving to discover a mean to increase the human life longevity. Besides your remarkable “phagocytes” you should think about the Bulgarian yoghurt and this rod-like bacillus discovered from Stamen Grigoroff, which I have also observed microscopically. It might be useful for your studies.”.


During his investigation, Stamen Grigoroff discovered two more bacterial species: streptobacillus and micrococcus - Streptococcus thermophilus. They co-exist with the lactobacilli in Bulgarian yoghurt in natural symbiosis.


History of Kefir in Short

Kefir is a drink made of fermented milk — not unlike yogurt — whose origins lie with nomadic shepherds living on the slopes of North Caucasus Mountains. Today, kefir is the most popular fermented milk in Russia. Late in the 20th century, kefir accounted for between 65% and 80% of total fermented milk sales in Russia with a production of over 1.2 million tons per year in 1988.



Kefir’s popularity has spread from Eastern Europe so that it is now regularly consumed in North America, Europe, Australia, and the United Kingdom, where pasteurised kefir may be found in many stores and supermarkets. It’s also being produced on a large scale in countries that once made up the Soviet block, as well as Czechoslovakia, Hungary, Poland, Finland, Norway, Sweden, Switzerland, Germany, and even as far away as Southeast Asia. Known as yogurt de pajaritos (bird’s yogurt), kefir has also been enjoyed in Chile for over a century, likely brought to South America by waves of immigrants from Eastern Europe or the former Ottoman Empire. Flavored varieties have been developed and are especially popular in the United States.


There is a legend among the Islamic people living on the northern slopes of the Caucasus Mountains that Mohammed gave kefir grains to Orthodox Christians, thereby teaching them to make kefir. Called the “Grains of the Prophet,” they were jealously guarded by their owners, as they believed the grains would lose their potency if the secret of their use became common knowledge. Thus, kefir grains were secretly passed from one generation to the next, closely guarded as part of the wealth of each family within the tribe, and although foreigners were sometimes given kefir to drink—Marco Polo recounts tasting kefir in the book of his eastern travels—the method of making kefir was kept secret, and the drink was all but forgotten until the 19th century.



It cannot be overlooked that kefir grains indeed can be described as “magical”: Despite intensive research spanning well over a century and many attempts to produce kefir grains from pure or mixed cultures typically found in the grains, no successful results have been reported to this day, likely because so very little is known about the way in which the kefir grains form.



The most ancient methods of making kefir were far from complicated: fresh milk—from cows, goats, or sheep—was poured into watertight bags made of goat or sheepskin and the “magical,” cauliflower-like grains of a kefir culture were added before the bag was suspended in the sun during the day. When the sun went down, the bag was brought inside and hung near the door. Each person passing in or out of the doorway would push or prod the bag, helping ensure that the milk and kefir grains remained well mixed with the milk fermented. As kefir was consumed, more milk was added to the bag so that the process could continue uninterrupted—as it had for hundreds or even thousands of years, descended through the ages from kefir grains first used many generations ago.