kaymak vs sour milk

kaymak

noun
  • A creamy dairy product, similar to clotted cream, made in the Balkans, Turkey, the Middle East, Central Asia, Iran, Afghanistan, and India. It is made from the milk of water buffalos in the East or of cows in the West. 

sour milk

noun
  • A kind of dairy product produced by causing raw milk to somewhat congeal by addition of acid or fermentation through bespoke acidification cultures. 

How often have the words kaymak and sour milk occurred in a corpus of books? (source: Google Ngram Viewer )