Daf ha-kashrus

Steam Heating – Lo Basi Ela L’Orer

Vol. 22 / No. 10

by Rabbi Eli Gersten

Although the term “kli rishon” conjures up in our minds a picture of a pot sitting on a flame, in reality in most modern industrial settings the kli rishon refers to a vessel that is heated by steam. Whether it be through steam jacketed kettles, direct steam injection, or hot air blown off of steam coils, most often steam has become the heat source of choice. Although steam is perhaps a more efficient form of cooking, still cooking with steam introduces us to a new set of complexities and shailos.

Is a steam heated pot a kli rishon?

The Avnei Nezer  (Y.D. 111) was asked about whether one can do hagalah by immersing  one’s chametz pots in a kettle that is heated with direct steam injection. Is it acceptable to kasher pots that were heated directly on a fire, by boiling them in a steam heated kettle? He answers that since steam has the ability to boil the kettle of water and to keep the water hot so it cannot cool down, this would be a full kli rishon, and can be used for kashering pots for Pesach1.

Is steam considered aish or toldos ha’aish?

The Sharei Teshuva (O.C. 451:27) writes that if issur was placed on a pan after it was removed from the fire, it would be enough to kasher the pan with libun kal. Had the pan remained on the fire, it would require libun chamur, but since it was removed, it is now only a toldos ha’aish, and when kashering from bliyos caused by a toldos ha’aish, it is enough to kasher with libun kal. The same sevara perhaps can be applied to a steam heated vessel. A steam heated dryer or oven is perhaps more similar to a toldos ha’ish. This is because the steam by the time it is used is no longer being heated by the fire.  The steam travels tens of feet away from the boiler and the fire no longer has any direct effect on the steam. It is merely a toldos ha’aish, giving off the heat it absorbed earlier. Rav Belsky and Rav Schachter have said that in this type of case, when the kli is an aino ben yomo, we can kasher with libun kal.

Is cooking with steam bishul akum?

The Issur V’Heter (43:16) writes that fish that was cooked through hot smoking is not subject to bishul akum. Many Achronim (see Yebiah Omer Y.D. 5:9) extended this heter to cooking with live steam as well. The OU has been lenient regarding live steam provided that this is done in a factory setting, with specialized equipment that would cook differently than one would at home. Tuna fish that is first cooked with live steam would not be bishul akum. However, the OU is not lenient regarding foods cooked in the can in a steam retort. Even though this form of pressurized cooking can be considered specialized equipment, however, the cooking is done by the water in the can and not directly by the steam.

Nitzuk chibur

Often a plant will have only one boiler that it uses for cooking in multiple areas. If one kettle is used for kosher and another is non-kosher, can both kettles be allowed to receive steam at the same time?

If one pours a bottle of kosher wine into a cup of yayin nesech, although we know that none of the yayin nesech flows backwards up into the bottle, nevertheless we view the connection formed as though it is a mashehu. Since yayin nesech will assur wine b’mashehu, this nitzuk is enough to make the bottle of wine forbidden. But this is limited to issurim, such as yayin nesech, which are assur b’mashehu. Although Rema 105:3 (as explained by Taz) says that lichatchila one should not create a nitzuk between heter and issur, when it comes to steam there are additional reasons to be maikel.

  1. Steam when it is in gas form is invisible. There could only be nitzuk through wet steam (zeiya), but dry steam is like hot air, and does not act as a chibur.
  2. In the case of boiler steam, the chibur is not direct between the heter and issur, but only between the outside jackets of the kettles. Rema 92:8 says that we are maikel regarding chibur of zeiya between two covered keilim.


Transfer of ta’am into steam

When steam comes in contact with the colder metal of a kettle or heat exchanger, it will condense into water. Although this water only touches the outside of the kettle, Shulchan Aruch (Y.D. 92:5-7) writes that we are choshesh that it absorbs ta’am from the food that is cooking in the pot. Therefore, the steam that is used to heat the treif kettle becomes non-kosher. If enough non-kosher steam condensate is returned to the boiler, the boiler will become non-kosher. The two main approaches to dealing with this issue are by:

  1. Not returning condensate from the non-kosher cookers. All such steam would be sent to the drain.
  2. Being pogem the boiler. This can be done by maintaining 5 ppm of Bitrex in the boiler.

One exception to this rule is non-kosher grape juice which is batel b’shaish in water.  We assume that whatever ta’am enters the boiler will always be batel. Additionally, the bliyos of grape juice are ta’am lifgam into the steam.

Other considerations

It should be noted that steam is a much more concentrated form of heat than hot water. One pound of steam contains 970 more BTU’s of heat than a pound of boiling water. This means that 1 lb of steam directly injected into 7 lbs of 72° F water will bring the entire mixture to a boil. Additionally, often only half the water in a boiler is return condensate, while as much as 50% is fresh city water. Therefore, if only a small percentage of the steam in a plant was treif, b’shas hadchak there is reason to assume that the tarfus is batel b’shishim, and we could be maikel on products that were already produced.


1. For more on this topic see Darchei Teshuva 121:16