sponge cake vs zwieback

sponge cake

noun
  • A light, soft, baked dessert (commonly layered with cream and jam) that is typically made with flour, sugar, baking powder and eggs, and has a firm, yet well aerated structure, similar to that of a sea sponge. 

zwieback

noun
  • A usually sweetened bread enriched with eggs that is baked and then sliced and toasted until dry and crisp; considered easy to digest and therefore given to the ill and used as a teething food for toddlers. 

How often have the words sponge cake and zwieback occurred in a corpus of books? (source: Google Ngram Viewer )