Lo Basi Ella L’orer: Cooling Water Systems

A common way to cool products is through the use of a cooling water system. In a cooling system, ambient or chilled water is used to cool hot products. The product transfers its heat with the cooling water (for example through the use of a heat exchanger) and then the water in turn is cooled. Most cooling systems accomplish this through the use of a cooling tower. Cooling towers make use of the cooling effect of evaporating water. Allowing a small portion of the water to evaporate into a moving air stream provides significant cooling to the rest of the water. While cooling towers are efficient ways of cooling water, they are also known to breed dangerous pathogens such as legionnaire’s disease. Therefore, although as we will discuss there are situations where we need to be pogem cooling water, under no condition should anyone taste cooling water חמירא סכנתא מאיסורא.

Shulchan Aruch (Y.D. 92:5) says “if a drop of milk falls on the outside of a pot (of meat) that is next to the fire … it can penetrate into the pot, and is as though it fell inside the pot”. Taz Y.D. (92:21) says that this halacha even applies to a kli rishon that was removed from the fire. Rav Belsky and Rav Schachter have said that this halacha does not apply to a kli sheini1. Let us see how to apply this halacha to a cooling water system.

Kli Rishon shelo al ha’aish:

If cooling water is circulated around a hot kettle even though the steam is off (kli rishon shelo al ha’aish) the water can be boleya ta’am from the kettle. If this kettle is not kosher, the cooling water will become non-kosher. If this water is recycled and then used to cool a hot kosher kettle, the kosher food can become non-kosher as well.

In this situation:

  • One must either drain the cooling system before a kosher production.
  • Or add a davar hapogem. Because cooling systems always lose a certain percentage of their water due to evaporation, fresh water is always being added.

Therefore, a davar hapogem (such as Bitrix) must be metered in with the fresh water to retain the proper level of pegima at all times. The OU works with certain boiler maintenance companies that can set up metering systems. (As mentioned earlier one should not taste the water from a cooling system to see if it is sufficiently pagum, since it may contain harmful bacteria.)

Cooling water in a heat exchanger:

A very common method for cooling products is with a heat exchanger. Hot product is pumped from the kettle through the product side of the heat exchanger while cool water is pumped through the opposite side. If the walls of the heat exchanger become saturated with heat, we will treat the heat exchanger like an extension of the kli rishon and cooling water that shares a wall with the assur product will become assur.

However, if the cooling water exits the heat exchanger while it is still below yad soledes, then we assume that the entire thickness of the plate did not become hot and no ta’am transferred to the water. For example, in one cooling system that was reviewed recently, the cooling water entered the heat exchanger at 80 F and exited at 90 F. Although the non-kosher product being cooled was 200 F, the company did not allow the cooling water to increase more than 10 degrees since their cooling tower only had 10 degrees of cooling capability, and the cooling equipment was not rated for hot temperatures. Every cooling system is different but this is a question that is worth asking.

Another common scenario involves chilled water that is used to cool product after it has initially been cooled in a regen system. HTST pasteurizers typically have a regeneration section (hot product against cold product) to most efficiently heat and cool. Though it is difficult to determine the exiting temperature of the product from the regen section, still even if it were surely above yad soledes, at this point the product is no more than a product exiting a kli sheini. It has already lost much of its heat as it traveled through the regen section with its difanos mikareros. When it finally enters the chilled water section it can no longer cause a bliya through the walls. In this case there is no concern of recirculation.

Cooling bath:

Cans exit a retort and are dropped into a cooling bath. This is a situation of cham l’toch tzonen and only a k’dei klipa of water can become assur. So long as the water in the bath always remains below yad soledes, Rav Belsky has said that we need not be concerned that the water becomes assur. He considers the kdei klipa in this case to be like a mashehu. Even thousands of these kdei klipos are still such a small amount that we can assume that they will always be batel in the overall bath.


  • Cooling water against a hot pot can transfer ta’am
  • In such cases the cooling water must be drained or made pagum
  • Cooling water through a heat exchanger where the water gets above yad soledes transfers ta’am.
  • If the water remains below yad soledes, there is no transfer of ta’am.
  • If cooling water cools product that was initially cooled, such as in a regen system, it is like a kli sheini and will not transfer ta’am.
  • A cooling bath for cans is not a problem, so long as it always remains below yad soledes.


  1. Irui kli rishon into a kli is only maflit a kdei klipa of the kli. The liquid in the kli is then considered a kli sheini and is not more chamur than the irui. Similarly, when kashering a kli sheini it is sufficient to kasher with irui, since that is how the bliya entered.
OU Kosher Staff