clabber vs sour milk

clabber

noun
  • Sour or curdled milk. 

  • Wet clay or mud. 

verb
  • To sour or curdle. 

sour milk

noun
  • A kind of dairy product produced by causing raw milk to somewhat congeal by addition of acid or fermentation through bespoke acidification cultures. 

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