Is DIY yogurt really safe?

After interviewing relevant experts, we found that there are several major concerns about home-made yogurt -

The conditions for homemade yogurt are limited, and hybrid bacteria can take advantage of the situation.

Generally speaking, The yogurt produced in the factory must go through a strict process. For example, when producing solidified yogurt, fresh milk must go through many processes such as milk purification, standardization, ingredients, preheating, homogenization, sterilization, cooling, inoculation of starter culture, filling and sealing, fermentation, cooling, and post-ripening. The production of stirred yogurt is slightly different. The initial process is similar, and then it is fermented in a large tank, stirred and broken, cooled, filled or mixed with spices and fruits before filling.

In the complex process of producing yogurt in factories, sterilization is an important step. The purpose of sterilization is to remove harmful bacteria in raw milk, reduce redox reactions, and improve the hardness and structure of milk.

Sterilization should be carried out at 90°C for 5 to 10 minutes. The sterilized mixture must be cooled to 40 to 45°C for later use. Or use high-temperature sterilization, heating at 120°C for about 3 to 5 seconds. This will help preserve nutrients and reduce boiling odor.

Strain preparation and fermentation are key technologies for yogurt production. During the fermentation process, the production starter made from a pure culture of lactic acid bacteria is fermented in an environment of 42 to 45°C, which is the optimal growth temperature for a mixture of Lactobacillus bulgaricus and Streptococcus thermophilus. Inoculum size, starter activity, and culture temperature are the three factors that require most attention during production.

When making homemade yogurt in a home environment, first of all, strict sterilization conditions cannot be guaranteed. Even if the milk is boiled and all the utensils related to preparing yogurt are sterilized in boiling water, it is easy to be contaminated by other bacteria during the operation. contamination; secondly, if a constant-temperature container is not used, yogurt cannot always be fermented in an environment of 42 to 45°C.

"As netizens said, it is not advisable to ferment yogurt in a thermos cup, or to place the container in a heating pipe or in the trunk of a car. First, it is difficult to control the temperature, and second, it takes several hours to make homemade yogurt. After fermentation, it becomes solid. If it is not processed in time and placed in the refrigerator, hybrid bacteria can easily mix in," said Nan Qingxian, a professor at China Agricultural University and a famous livestock product processing expert. "It is more dangerous to drink yogurt with more hybrid bacteria. , you will almost get sick if you drink it, especially if you don’t give it to children.”

There are hidden concerns about self-purchased strains

When people share their experience in making homemade yogurt, they often mention it. I bought a yogurt machine and some strains myself. Some unheard of strains such as snow lotus strains, Tibetan mushrooms, Caucasian kefir, etc. have appeared on the Internet, making the originally numerous yogurt strains even more difficult to identify.

Some strains of bacteria packaging also display slogans such as "Probiotics, Bifidobacterium, special for home-made yogurt, the only QS certified bacteria powder". In fact, the safety of self-purchased strains, especially those purchased online, cannot be guaranteed. Whether these purchased inoculants are truly QS certified remains to be discussed. Some inoculants do not even have labels on the manufacturer or place of production.

Self-purchased strains are usually presented in powder form, and ordinary people cannot visually identify whether the strains are mixed with other bacteria. The strains purchased online are extremely easy to deteriorate due to the influence of temperature during transportation. As a result, adding bacterial powder to homemade yogurt has no effect at all. Or yogurt is made from "inauthentic" strains of bacteria, and it is impossible to tell whether the yogurt is safe with the naked eye.

Nan Qingxian said that the bacteria for homemade yogurt should be purchased from regular merchants as much as possible. When purchasing, you should read the ingredients of the bacteria, the manufacturer, whether there is a QS mark, the production date, etc.

“If you want to make your own yogurt, it is not recommended to buy strains online. You can choose commercially available big brand yogurt as strains. Do not buy yogurt made by small workshops as strains. Be careful not to reuse homemade yogurt multiple times. Yoghurt is used as culture because miscellaneous bacteria will breed.”