clabber vs lopper

clabber

verb
  • To sour or curdle. 

noun
  • Sour or curdled milk. 

  • Wet clay or mud. 

lopper

verb
  • To turn sour and coagulate from too long standing, as milk. 

noun
  • A person who lops. 

  • A gardening tool used for lopping. 

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