cork up vs keep back

cork up

verb
  • to enclose in a bottle sealed with a cork 

keep back

verb
  • To hold back; to refuse to give or share. 

  • To restrict or restrain. 

  • To prevent (a pupil) from advancing in a course. 

  • To stay back; to refrain from approaching. 

How often have the words cork up and keep back occurred in a corpus of books? (source: Google Ngram Viewer )