SOURCE: Bernstein, Jüdische Sprichwörter und Redensarten. A shtreimel is a fur-trimmed hat traditionally worn by rabbis and Hasidic Jews on the Sabbath and holidays. And of course the pig is ritually unclean. Compare:
.פֿון בלויז וואַסער קען מען קיין קרופּניק ניט קאָכן
Fun bloyz vaser ken men keyn krupnik nit kokhn.
You can't cook barley soup with just water.
SOURCE: Stutchkoff, Der Oytser fun der Yidisher Shprakh.