Is the yogurt bad if it is particularly sour?

Sometimes you may find that your yogurt tastes particularly sour, and then you will think that your yogurt has gone bad. But in fact, if it has not exceeded the shelf life, it will generally not go bad. However, you must pay attention to the storage temperature. It can only be stored in the refrigerator and must not be stored at room temperature. Otherwise, it is very easy for the yogurt to deteriorate and it cannot be eaten.

Identification of yogurt: High-quality yogurt is milky white or light yellow, finely coagulated and free of bubbles. The taste is sweet and sour and fragrant. Spoiled yogurt is often dark yellow, green, gray, has uneven curds, and contains bubbles. If the taste is sour, with a spicy or musty smell, it indicates contamination by bacteria and is not suitable for consumption.

The quality of yogurt does not depend on its thickness. The production of yogurt requires pretreatment such as homogenization and sterilization, adding about 7% sucrose, and then inoculating specific lactic acid bacteria that have been cultivated in advance and keeping it warm at around 42 degrees Celsius. Lactic acid bacteria multiply in large numbers by relying on the nutrients in milk and produce lactic acid and aromatic substances. The protein in milk has the property of coagulating when it encounters acid, and under the action of lactic acid bacteria, it gradually turns into a uniform, fine and fragile gel. When the acidity is right, the yogurt is transferred to 4 degrees Celsius and the activity of lactic acid bacteria stops. The yogurt sold directly at this time is called set yogurt. The solidified yogurt can be stirred slowly to obtain a uniform semi-solid flowable product, which is stirred yogurt.

Slow stirring will not destroy the protein colloid, so the product is delicate and has a certain consistency. If stirred quickly, the protein colloid will be destroyed and the product will become thinner. Stirred yogurt made from pure milk is not very viscous and still has a certain fluidity. Some products also use milk and milk powder as raw materials. The protein content in the product is higher and it is more viscous. In order to increase the thickness of yogurt, a variety of thickeners such as gelatin or dietary fiber can be added during the production process. Gelatin is a protein colloid, which is the main ingredient in meat skin jelly and can be digested and absorbed by the human body.

Dietary fiber thickeners include alginate, pectin, plant seed gum, cellulose derivatives, etc. They are harmless to the human body, have no calories, and can play the beneficial role of dietary fiber. It can be seen that the consistency of yogurt has no direct relationship with its nutritional value. When consumers purchase, they should pay more attention to the protein content indicated on the packaging. Generally, the protein content of stirred yogurt made from pure milk is above 2.3%. If it is lower than this value, it cannot be called yogurt.

There are also many lactic acid beverages on the market that are slightly thinner than yogurt and have a sweet and sour taste. They are not in the same category as yogurt, have a protein content of just over 1%, and have a nutritional value far lower than yogurt. Consumers should note that although these products have many names, they all have the word "beverage" marked in small print, proving that they are not yogurt and should be carefully distinguished.