There are many kinds of dairy products on the market, and there are many. How to choose correctly? Let us first understand the common milk and its products.

　　 1. Sterilized liquid milk

　　 Sterilized liquid milk is the most common and most consumed milk. According to the difference in sterilization temperature during processing, liquid milk is divided into two categories, namely pasteurized milk (referred to as "pasteurized milk") and ultra-high temperature sterilized milk. The pasteurized milk adopts the "pasteurization" method, that is, the heating temperature is low during disinfection, ranging from 70 to 90°C. The heating temperature of ultra high temperature sterilized milk is relatively high, mostly 130～145℃. The higher the heating temperature, the more damage to vitamins, especially vitamin C and vitamin B1. Therefore, it is generally believed that the nutritional quality of pasteurized milk is better. Of course, for the nutritional quality of milk, the quality of the milk source is more critical than the processing technology (such as sterilization temperature and time). The advantage of ultra-high temperature sterilized milk is that it has a long shelf life, which can be preserved for more than 30 days without refrigeration. It is more convenient to buy or eat. Therefore, it has been popular with consumers in recent years and has occupied most of the market share.

　　 2. Yogurt

　　 Yogurt generally refers to yoghurt, which uses milk (fresh milk or powdered milk reconstituted with water) as raw material, after sterilization (pasteurization or high temperature sterilization) , Add bacterial fermentation to the milk, and then cool the filled milk product. At present, there are many types of coagulation type, stirring type and fruity type.

　　The fermenting bacteria for making yogurt have been mainly Lactobacillus bulgaricus (L) and Streptococcus thermophilus (S). In recent years, in order to open up the market, many products have added other so-called probiotics on the basis of using these two traditional fermentation bacteria, that is, bacteria that are beneficial to health, such as bifidobacteria (abbreviated as B), Lactobacillus acidophilus (abbreviated as A ) And multiple strains belonging to them, or some special health strains that have been bred, such as a certain Lactobacillus rhamnosus (LGG), etc. Fermentation bacteria or probiotics of the above-mentioned different strains or strains have different effects on the flavor of yogurt products, but the health benefits are basically the same, mainly to promote the reproduction of beneficial intestinal flora, inhibit the growth of harmful bacteria, and improve constipation. Improve body immunity.

　　The flour is fermented to make steamed buns, which is easy to digest and absorb. The fermentation of milk into yogurt also has the same effect. Fermentation makes the protein molecules smaller (decomposed), which is easier to digest and absorb; fermentation also synthesizes a small amount of B group Vitamins and promote the absorption of minerals. Yogurt not only retains the nutritional advantages of milk, but also improves the nutritional value due to fermentation. The live bacteria (fermentation or addition of probiotics) in yogurt also has a certain health care effect. Therefore, yogurt has been widely recommended, known as "longevity food" or "the most ideal food", suitable for everyone to drink, especially for constipation, indigestion, the elderly and children. And because the content of lactose in yogurt is very low (fermentation bacteria convert lactose in milk into lactic acid), it is suitable for those who are lactose intolerant.

　　 Yogurt can be made by a family yogurt machine. There are various types of yogurt machines on the market. The basic principle is very simple. It is to maintain a suitable constant temperature (about 40°C, 6 to 10 hours) to ferment the milk. As long as it is used correctly according to the instructions of the yogurt machine, the taste and hygienic status of the produced yogurt is not inferior to that of commercially available yogurt, and the nutritional quality is more reliable.

　　It should be noted that: ① Yogurt can not be heated and drink, once heated, the active lactic acid bacteria contained in it will be killed, not only loses the health care function, but also has a bad taste. ② Yogurt needs to be refrigerated and stored under high temperature, because the live bacteria in it are still fermenting, the acidity of yogurt will continue to increase and will become more acidic until it deteriorates. When buying yoghurt in the hot summer, be sure to see if the yoghurt is kept in the freezer, otherwise it is difficult to guarantee the quality. ③ Children should rinse their mouths after drinking yogurt, because the lactic acid in yogurt will corrode the teeth and increase the risk of children''s dental caries. It is best to use a straw to reduce the chance of lactic acid touching the teeth.

　　 3. Milk powder