Something non-kosher ends up in a pot of kosher food. The halacha has a framework for that, and it is one of the most misunderstood areas in kashrus — usually in the direction of assuming it applies far more widely than it does.
The basic rule
Where a forbidden substance is mixed into permitted food and is outnumbered by a sufficient proportion — generally sixty to one — it is nullified. The food does not become forbidden.
The reasoning is about taste: at that proportion the forbidden substance no longer contributes any perceptible taste to the mixture, so there is nothing of it left in any meaningful sense.
What it does not apply to
This is the part that matters, because the exceptions are where real cases live.
A whole creature. A beryah — a complete creature, such as an intact insect — is never nullified by any ratio. Its wholeness is what makes it significant, regardless of size. A fragment is not a beryah and can be nullified.
Anything removable. If the forbidden item can be picked out, it was never really mixed in, and the question of proportion does not arise. It simply has to be removed. This applies even to a fragment.
Chametz on Pesach. Prohibited in any amount. There is no proportion that suffices.
Things that are meant to be there. A substance added deliberately for a purpose — to flavour, to colour, to stabilise — is doing a job in the food. Something that is performing its function has not been nullified, whatever the ratio.
That last principle has a useful converse: where a substance genuinely serves no purpose in the final mixture — present only as a carrier from an earlier stage, contributing nothing — the analysis is different, because nobody intended it to be there and it is not doing anything.
You may not do it on purpose
Ein mevatlin issur l'chatchilah — one may not deliberately nullify a prohibition. You cannot take forbidden food, add sixty times as much permitted food, and serve the result.
This is the rule that stops nullification from being a technique. It exists precisely because the arithmetic would otherwise make the prohibition meaningless.
It is a rabbinic rule rather than a Torah one, which matters in how edge cases are analysed — but it is not a soft rule, and it is why a certifying agency cannot approve a process whose purpose is to dilute a problem away.
Where this leaves you
If something has gone into a pot, the honest answer is that you cannot work this out yourself. The questions that decide it — what went in, how much, whether it is removable, whether it is a beryah, whether it was hot, whether the pot was ben yomo, what it is doing in the food — interact, and the answer to one changes the relevance of the others.
This is the classic "stop and call your rav" situation. Do not throw the pot out and do not serve it; ask.
See also checking vegetables for insects, where the beryah rule does most of the work.
Where this comes from
- Shulchan Aruch, Yoreh De'ah 98 and 99, on nullification in sixty
- Shulchan Aruch, Yoreh De'ah 84, on a beryah
- Shulchan Aruch, Yoreh De'ah 99:5, on ein mevatlin issur l'chatchilah
- Responsa of Rav Schachter on carriers and on intent to nullify