The starter for the Yogurt culture is digestive bacteria comes from one’s own saliva.
While using Edible peppermint alcohol mouthwash one can drink to cleanse the palate and then take a sip of milk and the milk will curdle after a while into a clean smelling and tasting yogurt.
Or you can buy the yogurt culture , Bulgarian is the kind whose use is so famously by centenarians.
“Bulgarian yogurt, or kiselo mlyako, is one of the healthiest foods known to mankind. It is the particular combination of its two strains, lactobacillus bulgaricus and streptococcus thermophilus, that makes the yogurt unique in taste, thickness, acidity and aroma.
It is truly like nothing you have tasted before.”
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There are many many other cultures too. But the kind you are asking for is Bulgarian.
“People who have tasted yogurt from countries all over the world always find that none of them tastes anything like the Bulgarian variety. Bulgarians completely agree that their yogurt is the best – some 400 000 tons are consumed every year in the country.”
Human saliva , like some lime juice expectorated into the milk is also traditional method.
It is how we produce Traditional Sake.