Where does “crustans” come from?

crustans (Latin) comes from Latin crusto, from Latin crusta, from Proto-Italic *krustos, from Proto-Indo-European krustós, from Proto-Indo-European krews- — to form a crust, begin to freeze.

Definitions

Ancestry of “crustans”, step by step

Step	Language	Word	Meaning
1	Latin	crusto	I cover with a rind, shell, incrustation,...
2	Latin	crusta	The hard surface of a body; rind, shell, crust,...
3	Proto-Italic	*krustos	—
4	Proto-Indo-European	krustós	hardened
5	Proto-Indo-European	krews-	to form a crust, begin to freeze

Every word from Proto-Indo-European krews- →Every word from Proto-Indo-European krustós →Every word from Proto-Italic *krustos →