OT: "sour lesson" a calque of German idiom?

[Amy West]

I have a native German speaker in a class, and she just used the
phrase "sour lesson" in an assignment. ("The Little Red Hen teaches
her friends a sour lesson by eating the bread herself.") Is this a
calque of a German idiom? (I haven't a dictionary of German idioms at
hand, otherwise I'd check.) If so, is it "saure Lehre"? Is it perhaps
just a substitution of "sour" for "bitter" in "bitter lesson"?

---Amy West

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