A sweet, not sour, New Year
The Chofetz Chayim has it in for borscht on Rosh Hashanah. It’s a close call for pickled herring as well. ...יש נמנעים לבשל בר"ה מיני חומץ בארש"ט וכדומה וע"כ האוכלים דגים לסימנא שיפרו וירבו כדגים אין מבשלין אותן בחומץ. “…there are those who refrain on Rosh Hashanah from cooking sour foods, such as borscht. Therefore, those who eat fish as a sign of fertility should not cook them in vinegar.” – Mishna Berura 583:5
Granted, this passage reflects custom more than law, but for