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A lot has been written about the benefits of living bacteria contained in yogurt. In addition, yogurt is easy to prepare at home. Housewives in full share recipes on YouTube, and especially curious even consider the resulting substance under a microscope and are amazed by what they saw.
As it turns out, a number of interesting chemical processes occur in the production of yoghurt. In fact, this is a controlled process of coagulation of milk, which is caused to deteriorate in a certain way.
In order to lay the foundation for the necessary final consistency of yogurt, in industrial conditions milk is mixed in an apparatus similar to a washing machine.
As a result, the structure of milk changes – large fat balls are broken into many small droplets. Then, the proteins contained in milk envelop each drop of fat.
Later, when the milk starts to curdle, and the proteins – stick together, the fat more evenly distributed throughout the product.
Then the milk is heated to kill any remaining harmful bacteria in it, and also to start the process of unfolding the protein molecules, which in this case form a lattice – the basis of the yoghurt structure.
To what temperature it is necessary to heat the milk and how long the process should last, depends on the desired taste of the final product.
In industry, as a rule, the temperature is brought to 85 ° C and the milk is left for 30 minutes, or 90-95 ° C for 5 minutes.
As one yogurt maker at home says, “when milk is heated to temperatures below 76 ° C, the consistency of yogurt will be more liquid, and the taste is more fresh, with fruit notes, and more tart, and if you bring the milk temperature to 90 ° C and stand it for 10 minutes, yogurt will be noticeably more dense and less tart, with a light creamy, nutty and egg flavor. ”
After cooling the heated milk to about 37 ° C, the most important, in the opinion of many, process in the production of yogurt is fermentation.
This temperature is favorable for the life of the two most commonly used bacteria in the preparation of yoghurt
products
During the process of reproduction, bacteria convert lactose (sugar contained in milk) into lactic acid, with an increase in the content of which the acid-base balance of milk begins to decrease.
Milk proteins respond to this change. Until now, they were in a “stuck together” state – either in the form of a shell of droplets of fat, or in separate small clots.
This state of proteins was stable due to the presence of a salt in milk, known as calcium phosphate.
Now, with a decrease in the acid-base balance, this salt dissolves, and the clots of proteins begin to disintegrate.
Individual proteins form a lattice, the cells of which capture droplets of water and fat. So the milk turns into yogurt.
The fermentation process is stopped by cooling the yogurt, resulting in a gelatinous mass.
In the production of filtered yogurt like the Greek, there is another stage in which the “jelly” is stratified by stirring, and then water, sugar and proteins are separated from the final product in the form of whey.
On a consistence such yoghurts are more similar to cottage cheese. But even in yoghurts, which do not use mixing and straining, the final texture is affected by everything – from the method of heating milk to its protein content.
Used, for example, a consistometer – a device for determining the density of yogurt by measuring the time for which the yoghurt mass crawls a certain distance along the wall of the glass beaker.
There are still viscosimeters that measure viscosity (some of them resemble tiny mixers), as well as a penetrometer for measuring the permeability of viscous bodies – here they simply throw the weight in yogurt from a certain height and measure how deep it has sunk.

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