Fermentation Lab Reports‎ > Yogurt ( Mustafa ERSOY )


The aim of this experiment is to examine how the yogurt is produce and to analyse the significant factors on yoghurt fermentation by preparing different types of yoghurt which are produced by various amounts of milk powders and inoculum rates.


Generically known as cultured milk as they all derive from the action of bacteria on all or part of the Lactose to produce Lactic acid, carbon dioxide acetic acid, diacetyl, acetaldehyde and several other components that give the products the characteristic fresh taste an smell. The micro-rganisms used to produce Kefir and Koumiss also produce ethyl alcohol, giving these products the characteristic intoxicating effects associated with the consumption of alcohol.

Legend tells that yoghurt and Kefir were born on the slopes of Mount Elbrus in the Caucasus range of mountains, between the Black and Caspian seas. On the hot southern slopes a pitcher of milk belonging to a Turkish nomad was contaminated by a mixture of organisms that thrived in the warm milk (40 – 45c). The result was what the Turks call “yogurut”. The name “yogurut” was supposedly introduced in the 8th century and was changed in the 11th century to the current version “Yoghurt”. Legend suggests that Yoghurt can act as a preservative against human ageing, however no scientific evidence actually supports this theory. Undoubtedly a regular intake of the organisms found in yoghurt can have a beneficial affect to the digestive tract.

Similarly Kefir resulted from milk contaminated by organisms that preferred the cooler temperatures (25 – 28c) found on th northern slopes. Kefir as a name originates from the Turkish word “Kef” meaning pleasurable. Kefir contains several organisms the most famous being yeast that produce alcohol, however the maximum alcohol content is in the region of 0.8%.

The production of Lactic Acid from Lactose within the milk has a preservative effect on the milk as the lowered pH of the cultured milk inhibits the growth of putrefactive organisms. This effectively increases the shelf life of the product. On the “down side” the acidified milk provides an ideal growing medium for yeasts and moulds that can produce “off” flavours if they are allowed to infect the product.

Some people suffer from lactose intolerance due to the fact that their digestive system lacks enzymes needed to break down the Lactose to simpler sugars. In many cases cultured milk products where the Lactose has been partially broken down can be acceptable to sufferers of Lactose intolerance.

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