barm vs leavening

barm

noun
  • Foam rising upon beer, or other malt liquors, when fermenting, and used as leaven in making bread and in brewing; yeast. 

  • A small, flat, round individual loaf or roll of bread. 

verb
  • To spurge; foam 

leavening

noun
  • The process by which something is leavened. 

  • Synonym of leavening agent 

adj
  • Making light by aeration. 

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