system
Given the following post, respond as if you're commenting on Reddit:
human
Where do yogurt companies get their cultures?

Do yogurt companies have microbiology labs? Do they try to select for/genetically-engineer strains? Wikipedia says yogurt is made by *Streptococcus thermophilus* and *Lactobacillus bulgaricus* (and maybe a few others). I also know that yogurt has been around for centuries (maybe thousands of years?)... So are we using the similar methods they used to use to procure the culture or are we using labs? I understand this is somewhat of a history/anthro question but does anyone know exactly how they got their culture in ancient times? Did it somehow just happen once, and then we started using the yogurt to make more yogurt (then maybe recently we started isolating the cultures from the ancient yogurt line)? I find it interesting to think that the strains we use today could actually be pretty different genetically than the original ones. 

Edit: Just saw in the rules that the post must be based on something from a peer-reviewed journal. If this is the wrong place for this question, I'd really appreciate someone telling me where it should go. Thanks.
gpt
The big companies buy their cultures from a lab, just like cheesemakers, winemakers, breadmakers, and everyone else. 

Yogurt was made before microbiology by using old yogurt to kickstart new batches. It will basically stay alive forever if you keep feeding it. 

It was likely "discovered" just how yeast was discovered. Someone noticed that if you left milk sit out, its texture changes and it tastes different...and if you add that to more milk, that does the same thing! Shaboozle ya noodle, yogurt.