Yoghurt is made by introducing specific bacteria strains into milk, which is then fermented under controlled temperatures and environmental conditions. The bacteria ingest natural milk sugars and release lactic acid as a waste product. The increased acidity causes milk proteins to tangle into a solid mass (curd).
Today, many different countries claim yoghurt as their own invention. However, the word ‘yoghurt’ is of Turkish origin. The Turks adopted yoghurt most widely and put it to the most culinary use. By the 17th entury Istanbul had 500 yoghurt shops. The use of yoghurt by mediaeval Muslim Turks is recorded in the books Diwan Lughat al-Turk by Mahmud Kashgari and Kutadgu Bilig by Yusuf Has Hajib written in the eleventh century. In both texts the word ‘yoghurt’ is mentioned in different sections and its use by nomadic Turks is described. Arab, European and African countries under Turkish Muslim rule took to yoghurt and it is widely eaten in places like Arabia and east Europe. Until the 1900s, yoghurt was a staple in diets of the South, Central and Western Asian, South Eastern and Central European regions.
Immigrants from the former Ottoman Empire territories introduced yoghurt to America and began producing it commercially. Yogurt's popularity in the United States was enhanced in the 1950's and 60's when it was presented as a health food.