Yaourt is simply the milk turned sour and somewhat resembles curds only that it is thicker in consistency. The milk is originally turned by introducing a few drops of the milk of the fig into a bowl of sheep or goat's milk gently heated and then allowed to cool. A spoonful of the yaourt is kept as a kind of leaven and is sufficient to convert a large bowl of milk into yaourt. Eaten with sugar yaourt is very palatable and refreshing in warm weather and is said to be a preventive of fever.
Source: wiktionary