Sour milk curdled with one of the LACTIC ACID producing bacilli, such as Lactobacillus acidophilus or Lactobacillus bulgaricus. It contains all the protein, fat, calcium, and vitamins of the original milk, and is therefore a nutritious food, but there is no evidence that it has any unique beneficial properties of its own. In countries where standards of hygiene are low, it has the advantage of having been sterilised by boiling and is therefore unlikely to be contaminated with dangerous micro-organisms.