Is homemade yogurt safe?

Self-made conditions are limited, and hybrid bacteria take advantage of it

Generally speaking, yogurt produced in factories has to go through strict technological processes. For example, when producing solidified yogurt, fresh milk should go through many processes, such as milk purification, standardization, batching, preheating, homogenization, sterilization, cooling, inoculation of starter, filling and sealing, fermentation, cooling and post-ripening. The production of stirred yogurt is slightly different, and the previous process is similar. After that, it is fermented in a large tank, stirred and crushed, cooled, filled or mixed with spices and fruit materials before filling.

sterilization is an important step in the complex process of yogurt production in factories. The purpose of sterilization is to remove harmful bacteria from raw milk, reduce redox reaction and improve the hardness and texture of milk.

sterilization should be carried out at 9℃ for 5~1 minutes, and the sterilized mixture must be cooled to 4 ~ 45℃ for later use. Or adopt high-temperature sterilization and heat at 12℃ for about 3~5 seconds. This is beneficial to the preservation of nutrients and reduces the boiling smell.

strain preparation and fermentation are the key technologies to produce yogurt. In the fermentation process, the production starter made of pure culture of lactic acid bacteria is fermented at 42 ~ 45℃, which is the optimum growth temperature for mixed Lactobacillus bulgaricus and Streptococcus thermophilus. Inoculation amount, starter activity and culture temperature are the three most important factors in production.

At first, it is impossible to ensure strict sterilization conditions when making yogurt at home. Even if the milk is boiled and all the related utensils for preparing yogurt are sterilized in boiling water, it is easy to be polluted by other miscellaneous bacteria during the operation. Secondly, yogurt can't be fermented at 42 ~ 45℃ all the time without using a thermostatic container.

There are hidden worries about purchasing strains

When sharing the experience of homemade yogurt, people often mention that they bought yogurt machines and some strains. On the Internet, Saussurea involucrata, Tibetan kefir, Caucasian kefir and other unheard-of strains have appeared, which makes the original yogurt strains more difficult to identify.

Some strains also display slogans such as "Probiotics, Bifidobacterium, home-made yogurt, only QS certified bacterial powder". In fact, self-purchased strains, especially those purchased online at will, cannot be guaranteed in safety. Whether these purchased microbial agents are really QS certification remains to be discussed, and some microbial agents are not even marked by manufacturers and production sites.

Self-purchased strains are usually in the form of powder, and ordinary people can't visually identify whether the strains are mixed with other miscellaneous bacteria. Due to the influence of temperature, online shopping strains are extremely easy to deteriorate during transportation, which leads to no effect when adding bacterial powder to homemade yogurt. Or yogurt is made of "incorrect" strains, and the naked eye can't tell whether yogurt is safe or not.