Raw milk from a healthy cow cannot be kept warm for a long time due to favorable conditions for the growth of microorganisms. There is its sourness and deterioration. Even in the cold, the shelf life of raw milk is limited. Freshly milked milk must be filtered as soon as possible (to remove large impurities) and boiled. Boiling destroys pathogens present in milk (except for the usual non-spore-forming ones). The effectiveness of the destruction of these microorganisms depends on the duration of boiling. Boiling also destroys lactic acid bacteria. The benefits of boiled milk for the body compared to freshly milked milk are much less, but the shelf life is longer. Dairy cows can suffer from various contagious diseases (infectious inflammation of the udder, tuberculosis, foot and mouth disease), so it is necessary to boil milk, especially when it is purchased on the market.
To prevent curdling of milk, it is recommended to add a tablespoon of sugar to 1 liter of milk before boiling it. Milk is boiled in enameled or stainless steel pots; ceramic and earthenware pottery is also suitable for this purpose. Do not use copper and iron utensils. Copper and iron contribute to the oxidation and spoilage of milk fat.
On the surface of milk, when it is heated to 50 ° C, a foam is first formed, consisting of fats, minerals and milk protein casein, somewhat changed in chemical composition. At temperatures from 55°C to 80°C, albumin coagulates.
When milk is boiled, a sediment forms on the bottom and walls of the dish, which is a partially precipitated proteins. The longer the milk was stored before boiling and the higher its acidity, the more sediment is formed. It is not recommended to boil milk, for this it is regularly stirred or special dishes with a double bottom are used.
Prolonged boiling causes protein coagulation and destroys heat-sensitive vitamin C. In addition, calcium and phosphorus are converted into insoluble compounds that are not absorbed by the human body. Albumin during prolonged boiling coagulates, settles to the bottom of the dish and burns. Fats go from a state of fine dispersion to the form of oily sparkles that float to the surface. There are taste and visual deficiencies, reduced nutritional value of milk. Boiled milk should not be stored in the light, especially in bright sunlight. Light accelerates the yellowing of milk fat and destroys vitamin C. Intense sunlight destroys vitamin B2 (riboflavin).