Identification of yogurt High-quality yogurt is milky white or light yellow, with fine coagulation and no bubbles. The taste is sweet, sour and delicious, with fragrance. Deteriorated yogurt is often dark yellow, or green, gray, with irregular clots and bubbles. The taste is sour, spicy or musty, indicating that it is contaminated by miscellaneous bacteria and should not be eaten. Yogurt is not good or bad because it is thin and thick. To produce yogurt, it needs pretreatment such as homogenization and sterilization, adding about 7% sucrose, then inoculating specific lactic acid bacteria that have been cultivated for a long time, and keeping the temperature at about 42 degrees Celsius. Lactic acid bacteria multiply by nutrients in milk, and produce lactic acid and flavor substances. Protein in milk has the characteristic of acid coagulation, and gradually becomes uniform, delicate and fragile coagulation under the action of lactic acid bacteria. When the acidity is suitable, the yogurt is transferred to 4 degrees Celsius, and the activity of lactic acid bacteria stops. At this time, the yogurt sold directly is called solidified yogurt. A uniform semi-solid flowable product can be obtained by slowly stirring the solidified yogurt, which is called stirred yogurt. Slow stirring will not destroy the protein colloid, so the product is delicate and has a certain consistency. If it is stirred quickly, it will destroy the protein colloid and dilute the product. The stirred yogurt made of pure milk is not very sticky and still has some fluidity. Some products use milk and milk powder as raw materials, and the content of protein in the products is higher and thicker. In order to increase the consistency of yogurt, various thickeners such as gelatin or dietary fiber can be added in the production. Gelatin is a protein colloid, that is, the main component in skin jelly, which can be digested and absorbed by human body. Dietary fiber thickeners include seaweed gum, pectin, plant seed gum and cellulose derivatives. They are harmless to human body, have no calories, and can also play the beneficial role of dietary fiber. It can be seen that the consistency of yogurt is not directly related to its nutritional value. When purchasing, consumers should pay more attention to the protein content indicated on the package. Generally, the protein content of stirred yogurt made of pure milk is above 2.3%. If it is lower than this value, it cannot be called yogurt. There are many lactic acid drinks in the market that are slightly thinner than yogurt and taste sweet and sour, which are not in the same category as yogurt. The protein content is only above 1%, and the nutritional value is far lower than yogurt. Consumers should pay attention to the fact that although these products have many names, they are all marked with "beverage" in small print, which proves that they do not belong to yogurt and should be carefully distinguished.