Daf ha-kashrus

Lo Basi Ela L’Orer: ZEIYA

Vol. 22 / No. 9

By Rabbi Eli Gersten

Shulchan Aruch (Y.D. 123:24) says that wine alcohol which was distilled from stam yaynam remains assur b’hanah just like the wine itself.  Although the alcohol is just the collected zeiya (vapors) from the wine, zeiya of issur retains its status. Similarly, Shulchan Aruch (Y.D. 92:8) writes that zeiya that emanates from milk is milchig, and if this zeiya comes in contact with hot meat, it will create basar b’chalav. The general rule is that zeiya will have the same status as the liquid – זיעת משקים כמשקים. Pri Migadim (Seder Hanhagos ha’nishal II:37) questions whether this rule applies to solids as well, however Igeros Moshe (Y.D. I:40) paskens that one should not be lenient. So both by liquids and by solids, zeiya retains the same status as the original food.

Har Tzvi (Y.D. 84) asks, how is it that mei mei chalav (milk from which all solids have been removed) is only chalav d’rabanan, while zeiya from milk, which is almost pure H2O remains chalav d’oreisa. He answers, that so long as the steam is still connected to the milk, it retains its full status of milk. However, cow water (condensate of whey water) which is the water removed from whey during evaporation, once it is no longer connected to the whey, would be only chalav d’rabanan.

Zeiya in Ovens

Teshuvas ha’Rosh (20:26) writes that one may not place a pan of milk under a pot of meat in an oven, and if one did, the food would be assur. Although the Rosh holds that in general, a hot pot has the ability to push away zeiya and prevent it from being absorbed, but in this case the Rosh was concerned that the pan might block some of that heat, and zeiya will get absorbed. It is for this reason that one may not cook milk and meat, or kosher and non-kosher together in an oven.

Igeros Moshe (Y.D. I:40) explains that today’s ovens should be viewed as a sealed box, even though they are slightly vented, because the zeiya cannot dissipate fast enough. Therefore, even though the top of the oven is very hot, the zeiya will get absorbed. The Rosh only says that zeiya is pushed away from a hot surface if there is a colder place for it to go, but since the oven is closed, the zeiya will back up and get absorbed everywhere, including the ceiling and walls, even though they are  hot surfaces.

Zeiya or Reicha

Zeiya is the steam (vapor) that emanates from a solid or a liquid. Zeiya as mentioned above has the same status as the food itself. Reicha is the aroma of the food that is not accompanied by steam, and in most cases we say bidieved, reicha lav milsa (reicha is not a concern). However, there are numerous exceptions to this rule.

Some dry items when cooked will produce only reicha, or such a minimal amount of zeiya that it will dissipate immediately in the air. Igeros Moshe writes that if we see zeiya, even it is from a relatively dry item, we must be concerned. Because the guidelines for what is considered dry and wet can be subjective, as a policy the OU will assume that any item that is placed in an oven will produce zeiya, unless it is proven or obvious otherwise. Even in a large oven “tanur gadol” the OU would be concerned for zeiya, since the ovens are used in a manner in which they are filled to capacity with product, shelf upon shelf from floor to ceiling.

Example: Dairy cookies are baked in a rack oven. The OU would be concerned that the cookie dough produces zeiya, and because the entire cavity of the oven is filled with pans of cookies the cumulative effect would be that the zeiya will not dissipate, but will reach the walls.

Example: A company wants to do a test run of a single pan of dairy cookies in a large rack oven. In this case, the zeiya will dissipate before it reaches the walls or ceiling. Of course, the mashgiach must be present to make sure that the batch is small enough that it will not produce zeiya. In this case reicha would also not be a concern because in relation to a single pan of cookies, the large rack oven is a tanur gadol.

Example: An oven dryer is used to reduce the moisture level of powders. The powders that are put on pans are very dry to begin with. In this case, since we know there will be no zeiya or reicha in the oven, there will be no need to kasher the oven. The pans of course in all these cases will require kashering.

Kashering with Zeiya

Rav Moshe Feinstein zt”l (Igeros Moshe Y.D. 1: 60) writes that he is doubtful as to whether a kli that had direct contact with a non-kosher liquid can be kashered by immersing it into live steam instead of using boiling water.  This is because he was concerned that steam is not a liquid, and although steam may be hotter than the original liquid that was absorbed, it would not be k’bolo kach polto. Since the original bliya was with liquid, perhaps the plita must also be with liquid. However, Rav Moshe accepted that we can leave the kli in the steam until condensation forms all over the kli, since it would then be considered that the kli was kashered with boiling water. However, if the original bliya was only with steam then it is clear from the Pri Chadash (Y.D. 121:15) that we can kasher with steam as well, since in such a case we would say k’bolo with steam kach polto with steam.

A common example of where we kasher with steam is when kashering a microwave oven. If a non-kosher food was heated in a microwave oven, the surface that touched the food directly requires hagalah, but the walls and ceiling that only absorbed non-kosher zeiya, can be kashered with hevel (thick steam) by boiling water in the microwave for several minutes. The cup is moved over and the water is boiled a second time as well, so that even the space that was covered by the cup will get kashered.