sour cream vs yogurt

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. 

yogurt

noun
  • A milk-based product stiffened by a bacterium-aided curdling process, and sometimes mixed with fruit or other flavoring. 

  • Any similar product based on other substances (e.g. soy yogurt). 

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