In the proverb quoted in Ezekiel 18:2, what had the fathers eaten?

Answer: Sour grapes

"The fathers have eaten sour grapes, and the teeth of the children are set on edge." God said the soul who sins is the one who will die.

““What do you people mean by quoting this proverb about the land of Israel: ‘The fathers have eaten sour grapes, and the teeth of the children are set on edge’?”— Ezekiel 18:2 (BSB)