Where does “ζυμάριον” come from?

ζυμάριον (Byzantine Greek) comes from Ancient Greek ζύμη, from Ancient Greek ζέω, from Proto-Indo-European yes- — to foam; to boil.

Ancestry of “ζυμάριον”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	ζύμη	sourdough; leaven, beer yeast; yeast
2	Ancient Greek	ζέω	to boil, seethe, bubble; to heat
3	Proto-Indo-European	yes-	to foam; to boil