Yogurt can also expire?

For yogurt, flavor, taste, the number of live lactobacillus, the number of pathogenic bacteria are the most important indicators, and flavor and taste are closely related to the change of bacteria.

The growth of lactobacillus and other bacteria follows a similar trajectory: they stop growing for a period of time at first, proliferate rapidly, and die in large Numbers. Different bacteria, different initial content, different environmental conditions of temperature, the time of emergence of different stages will be very different.

In yogurt, lactobacillus occupies the absolute advantage, those we don't like miscellaneous bacteria, yeast, etc., at the beginning is just a spark. At the refrigeration temperature (the preservation temperature in the refrigerator), lactobacillus will have a few days of sluggish growth period, during which the number of lactobacillus hardly increases, and it has a certain inhibitory effect on other miscellaneous bacteria.

After a few days, the lactobacillus population will increase, and more lactose will be converted into lactic acid. There will even be a pale yellow liquid in the yogurt, which is the extracted whey containing the whey protein. At this time, the taste of the yogurt will change a little, but it is still edible.

If put for a longer time, lactobacillus greatly reduced, miscellaneous bacteria active, yogurt is not only not delicious, security is also a problem. If the raw material and the manufacturing process are properly controlled, the yogurt shelf life can be refrigerated for two or three weeks with acceptable quality and may not be eaten at room temperature for a few hours.