*yeasty \YEE-stee\ (adjective) –
1 : Of, pertaining to, or resembling yeast.
2 : Not yet settled or formed; immature or incomplete.
3 : Marked by agitation or change.
4 : Frothy or trivial; frivolous.
5 : Full of vitality; exuberant.
"In that yeasty time in the mid-sixties when I went to work as a reporter in Paris, the world was about to pop." — Raymond Sokolov, ‘Why We Eat What We Eat’
Yeasty is from yeast, from Middle English yeest, from Old English gist.