Milk is a drink which is loved by both adults, and children. It is useful to health and well satisfies thirst. But it is rather difficult to store milk - it can turn sour, change the structure and taste. Why it occurs and how to avoid it?
To understand the reasons of turning sour of milk, it is necessary to understand what represents this drink. Milk contains a set of useful substances. Its important component is an animal protein, also in its structure there are dissolved fats and sugar. All these components can serve as food for lactic bacteria. When bacteria begin to breed, in milk there are various chemical reactions, including protein turning. For this reason milk turns sour, that is gets denser and also is divided into two components - serum and more dense curtailed part. What provokes reproduction of bacteria? First of all, it is storage temperature. Room temperature is enough to provoke reaction. Therefore milk needs to be stored in the fridge or in other cool place if you want to keep its fresh. Also the risk of turning sour of milk can be reduced by means of special heat treatment. There are two types of similar processing - pasteurization and sterilization. At pasteurization, milk heats up to 60-80 degrees Celsius and is in such temperature condition from thirty minutes to an hour. After this process the period of storage of milk increases for several days because a considerable part of lactic bacteria perishes. One more way of preservation of milk is a sterilization. In this case liquid heats up to a boiling point. Such milk can be stored in a sealed package within several months. It is convenient, but there are also some minuses - useful properties of such milk decreases. At preparation of a dairy products the people often specially ferment milk. In this case chemical process begins because of addition in liquid of special lactic bacteria, for example, of a bifidus bacteria, for receiving a product with special characteristics.