gunpowder tea vs herb tea

gunpowder tea

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

herb tea

noun
  • A beverage (a tisane) made by steeping herbs (sometimes also includes other plants, such as spices), other than tea leaves, in hot water. Technically not a tea because it does not contain tea leaves. 

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