clotted cream vs sour cream

clotted cream

noun
  • A thick, sweet dairy product, made by skimming the thickened layer off the top of unhomogenized cream that has been heated and allowed to stand. Fat content is at least 55%. 

sour cream

noun
  • Cream which has been treated with a benign bacterium to turn it slightly sour, often used as a condiment, or a topping for baked potatoes. 

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