Jell-O vs jello

Jell-O

name
  • A brand of dessert made from gelatin. 

  • Any brand of fruit flavored gelatin dessert mix. 

jello

noun
  • A dessert made by boiling flavoured gelatin in water 

How often have the words Jell-O and jello occurred in a corpus of books? (source: Google Ngram Viewer )