The prohibition against mixing meat and milk, one of the most specifically Jewish eating rules, applies at a Torah level only to the two cooked together. Siman 91 in Yoreh De’ah takes on other ways the two can mix, and the extent of the issue thus created.

Mixing Without Cooking

The siman starts with the reminder that the contact of cold meat and milk mixes only at the surface. We do expect some of each will stick to the other [You got your peanut butter in my chocolate! You got your chocolate in my peanut butter!], but a rinse removes the problem. If a bag has slots for milk and meat foods, Chullin 107b tells us we can carry them together, need not worry they will touch. If they do, rinsing again solves any problems.

Complications, significant and not: Shach thought there would be no need to worry about transfer if both foods were dry. The cooked/raw status of the meat doesn’t affect our reaction, but were either food shamen, fatty, the spot where it touched a food of the other type would have to be washed with shifshuf (a more vigorous form of wiping, either with water pressure or one’s hands).

Knife pressure increases the likelihood of absorption, so if someone cut the fatty material onto the other, we would require washing and careful wiping to ensure all the material had been removed. Once we’re here, AH throws in that if wet blood, cold melted fat, or butter fell onto meat and congealed, we require careful washing and shifshuf gadol, a vigorous and careful wiping of the area.

Not Only Foods, Not Only Meat and Milk

Se’if two extends the rule to containers—should meat be stored in a milk container, and either was moist, we would need to wash both, to be sure none of the one remains on the other. Taking us away from basar be-chalav (meat cooked with milk) for a second, AH cites Taz, in turn quoting Maharshal, travelers err when they eat salted fish from non-Jews’ containers. They need to wash the fish first, to take off any residue from other foods stored there before.

Peeling the skin of the sardines solves the problem better than washing, even, in that it fully removes the layer where the prohibited material might have been found. The same rules apply to salted cucumbers (his phrase; did he mean pickles?) that Jews eat in non-Jews’ homes, on their utensils. Peeling them, placing the peels on the plate, the cucumbers/ sardines on the peels, avoids the problems.

Similarly, if a Jew can wash a non-Jew’s container, s/he can then use it to store cold food or drink, a useful leniency for travelers, who often did not have containers ready at hand. [In our world of disposables, and supermarkets, many of these concerns are no longer so pressing.]

Okay After the Fact Isn’t the Same as Ok

In se’if three, AH reminds us these rules are for after a situation has already occurred (or we wash containers before we use them). To mix meat and milk or prohibited and permitted expecting to wash them, or to leave cold on a prohibited platter is not allowed, even if all that is needed is washing, lest the person forget. He contrasts this to siman 1, regarding shechitah, where we allow ourselves to ignore certain concerns, because here we would be introducing a definite prohibition.

With a food we expect to wash anyway, like raw meat, AH seems to think we could rely on that washing. Peri Megadim limited the permission to a cold milk plate, but AH was unsure why it wouldn’t apply to foods as well (if we’re going to wash the meat carefully no matter what, why can’t we also leave it touching cold, dry cheese, he means). He does denigrate it as mecho’ar ha-davar, unseemly to give the impression we do not care if these mix.

Rules for Bread and Containers

In se’if five, AH shares a special rule for bread, if it touches meat, it may not be eaten with dairy, and vice-verse. Shach did not think washing the bread would work, because it absorbs particles too well to be cleaned off, although AH accepts Peri Megadim’s view that it does. Knives used to cut meat and then not carefully cleaned and wiped of all remaining fat would render a piece of bread fleishig, not to be eaten with milk.

For our last discussion (in this siman) of how to rectify cold mixing, se’if six presents the rules Chavvas Da’as articulated for use of prohibited utensils. A container used regularly to hold nonkosher items, even if cold and none of which stayed in the container twenty-four hours (which makes it kavush, halachically similar to being cooked in that container), can be wiped quickly for a one-time use with cold permitted materials. For more frequent use, or to use it for a hot item occasionally, we would need shifshuf gadol, a thorough washing/wiping.

Levels of Heat, As They Affect Utensils

If this container hosted hot prohibited materials, we cannot use it for hot kosher items, because heat causes absorption and emission, the kosher food will absorb some prohibited material. We might think we could ignore these concerns if the container is not ben yomo, has not been used in twenty-four hours (where tradition held the taste becomes pagum, somewhat deteriorated, making any prohibition rabbinic), or if we were going to only use it with cold, but regularly. Not so, because we worry the Jew will forget and use it with hot.

For occasional cold use, even spicy and liquidy items—qualities that increase the likelihood of absorption--wiping will be good enough. More thorough wiping alleviates concerns about regular use with cold foods, as long as the use for prohibited items had been only occasional.

A reminder: “Hot” in these instances generally means at a keli rishon level (the pot was on the actual fire), or even irui keli rishon, the heat of food being poured from the utensil in which it was cooked to another one.

Once it reaches that second pot/pan/plate, it is a keli sheini, with much lesser halachic ability to cause absorption/emission, and we will only worry about using it for our purposes if it was used regularly for prohibited food at this level of heat. Then, we treat it like it absorbed from a keli rishon, and require a fuller kashering.

In all the cold situations we have discussed, washing the food would help were we to use a container without the needed wipe/wash/both. Where the food is unwashable (like a liquid), after the fact, we can use it.

When Hot Foods Touch

The rules change significantly when one of the foods is hot. Here, a prime Talmudic rule is teta’ah gevar, the item on bottom shapes the interaction. If cold meat fell into a pot of hot milk, we assume the meat will have been heated by the milk and the two will fully trade taste. If the meat fell onto solid hot milk/cheese, there will still be spread of taste, but only in that spot. Where the top item was hot, the bottom item is assumed to cool it off, although we do assume a layer of taste will get into the bottom food before the top one cools down.

Teta’ah gevar has many details, starting with se’if eight, why we operate by rules when siman 98 seems to accept the validity of te’imat kefeila, a non-Jewish cook tasting the food and telling us whether it has any taste of other foods in it.

This is a long topic, as is teta’ah gevar and more, and very practical, so let’s do it next time.

Adapted from articles previously published on Torah Musings