Avodah Zarah 75

The mishnah on today’s daf, the last mishnah of tractate Avodah Zarah, is our primary source for the rules of kashering vessels:

One who purchases utensils from gentiles: Those whose manner is to immerse them, he must immerse them. To purge (with boiling water), he must purge them. To heat until white-hot in the fire, he must heat them until white-hot in the fire. The spit and the grill, he must heat them until white-hot in the fire. The knife, he must polish it and it is pure.

The principle expressed here is that however a utensil is normally used, that is the means by which it must be made kosher. The source is a verse in Numbers 31, where Moses declares: “Any article that can withstand fire — these you shall pass through fire and they shall be pure, except that they must be purified with water of lustration; and anything that cannot withstand fire you must pass through water.”

The one outlier case in the mishnah is the process of immersion. A beraita cited later on the daf makes clear that even non-Jewish vessels that have never been used and therefore have never come into contact with forbidden food must be immersed. This is seemingly connected not to flavor and cleanliness, but rather “converting” the vessel to Jewish ownership.

The other examples follow the principle articulated above: However a vessel is used is the manner through which it can be made kosher. So vessels that are used to boil liquid, like pots and kettles, are kashered by immersing them in boiling liquid. If they are used with dry heat, like grilling utensils, they are kashered with dry heat. And if something was only ever used with cold food, we assume it hasn’t absorbed flavor and therefore a mere rinse suffices to render it kosher.

The mishnah also lists the case of the knife, which is rather unique. Though it is not primarily used with dry heat, it is used with pressure, which we believe can absorb some flavor. So unlike other cases of cold contact, the knife requires not just rinsing, but also polishing.

The Gemara then makes a curious addendum:

And all (utensils) that one used before immersing and purging and heating them until white-hot, it is taught in one place forbidden, and it is taught in another permitted.

We have a general rule that non-Jewish utensils have to be kashered. But what if someone happened to use them without kashering them first? The Gemara here reports that we have contradictory rulings about whether food prepared in such utensils is permissible.

The Gemara replies:

This is not difficult. This ruling is according to the one who says (that if a forbidden substance) imparts flavor to the detriment (of the mixture), it is forbidden. That ruling is according to the one who says (that if a forbidden substance) imparts flavor to a permitted food to the detriment (of the mixture), it is permitted.

Seemingly, unkashered vessels always impart a negative flavor to food so the ruling on the food’s status hinges on a debate we covered earlier with regard to noten ta’am lifgam, imparting negative flavor. However, this resolution presents a difficulty:

But according to the one who says that that (if a forbidden substance) imparts flavor to the detriment (of the mixture) it is permitted, the utensils of gentiles that require purging, which the Merciful One renders forbidden (until they are purged), how can you find these cases?

If unkashered vessels always impart only negative flavor, and negative flavor doesn’t render the affected food prohibited (according to one opinion), then why would the usage of unkashered gentile vessels be forbidden in the first place?

Rav Hiyya, son of Rav Huna, says: The Torah renders forbidden only a pot that same day, as it does not impart flavor to the detriment (of the mixture).

Rav Hiyya clarifies that pots used in the past day do impart positive flavor, and therefore the usage of such pots is forbidden. Only after the pots have been left to sit for over a day does the absorbed flavor become negative-tasting.The Gemara asks:

If so, from that point onward the pot should be permitted!

There is a rabbinic decree that prohibits use of a pot that was not used by a gentile that same day, due to concern that one will use a pot used by a gentile that same day.

If only pots used in the past day impart positive flavor, and therefore have the capacity to forbid, why wouldn’t those who hold that forbidden substances imparting negative flavor don’t prohibit the mixture not allow the usage of pots more than a day old? The answer is that the prohibition of such pots is a gezeirah, a rabbinic decree. If people became accustomed to using old non-Jewish vessels that haven’t been kashered, they might very easily end up using unkashered vessels which had been used in the past day. Therefore, we prohibit cooking in any unkashered vessel, even those with negative flavor.

Read all of Avodah Zarah 75 on Sefaria.

This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on September 1, 2025. If you are interested in receiving the newsletter, sign up here.