Please see this link
What is the "official" definition of the term "yogurt"?
Under the standard of identity established by the U.S. Food and Drug Administration (FDA), in order for a refrigerated product to be called "yogurt," it must be produced by culturing permitted dairy ingredients with a bacterial culture, which contains Lactobacillus bulgaricus and Streptococcus thermophilus. In addition to the use of bacterial cultures required by the FDA standard of identity, live and active culture yogurt may contain other safe and suitable food grade bacterial cultures. No standard of identity exists for frozen yogurt products, but they too may contain live and active cultures.
The National Yogurt Association (NYA) established its own criteria for live and active culture yogurt in conjunction with its Live & Active Culture seal program. In order for manufacturers to carry the seal, refrigerated yogurt products must contain at least 100 million cultures per gram at the time of manufacture, and frozen yogurt products must contain 10 million cultures per gram at the time of manufacture. This level was based on a survey of leading research scientists involved in clinical studies of the health attributes associated with live and active culture yogurt.
The Live & Active Culture seal to all yogurt manufacturers whose products, both refrigerated or frozen, contain a significant level of live and active cultures.
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Please see this link for curd
1 litre Milk 1/2tsp curd
Milk should be boiled and cooled. Remove the cream (malai) from milk and warm it (not too much).
In a bowl add curd and milk, stirring well. Place it in a warm & cozy place for overnight or for 5-6 hours. When it is done refrigerate it for 1-2 hours for better results.
Note : If weather is too cool especially in winters cover the bowl with some woolen cloth. Preferably use casseroles in place of a bowl for better result. In summers it take less time to get done
(Rated by 9 Council Members)