gunpowder tea vs herbal tea

gunpowder tea

noun
  • A form of Chinese green tea in which each leaf has been rolled into a small round pellet. 

herbal tea

noun
  • A beverage made by infusing the leaves of various herbs, generally not including true tea (Camellia sinensis). 

How often have the words gunpowder tea and herbal tea occurred in a corpus of books? (source: Google Ngram Viewer )