acerbate vs clabber

acerbate

verb
  • To make bitter or sour. 

  • To exasperate; to irritate. 

adj
  • Embittered; having a sour disposition or nature. 

clabber

verb
  • To sour or curdle. 

noun
  • Sour or curdled milk. 

  • Wet clay or mud. 

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