Leaving Diced Onions in Sealed Packaging Overnight & Sakana

May I dice onions and place them in sealed packaging to avoid the sakana (danger) of eating peeled onions that were left overnight?

(A subscriber's question)

The Gemara (Niddah 17a) writes that there is a sakana to eat peeled onions that were left overnight, even if they were placed in sealed packaging. The only exception that the Gemara mentions is if part of the roots or the peel is left on the onion. Tosfos (Shabbos 141a s.v. Hani) writes that the sakana applies to diced onions as well. However, if there are other ingredients mixed in to the onions, Rishonim already discuss that one can be lenient. Igros Moshe (Y.D. III: 20) writes that industrial produced products are not subject to this sakana. So one may purchase frozen packages of diced onions.

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