Why is yoghurt acidic?

A type of bacteria called "Lactic acid bacteria" ferment milk sugars, lactose to produce lactic acid. Its PH is around 4-5 and therefore it is acidic. Depending on the age and… bacteria activity of the yoghurt, the inoculated milk can acidify the sugars enough to coagulate the proteins , resulting into a custard-like curd. (MORE)