If a kettle is used to cook a non-kosher product then the hot water or steam that was used to heat the kettle becomes non-kosher as well. Chazal tell us that we must be concerned that some non-kosher taste may pass through the wall of the utensil and leach into the product on the other side. This is based on the halacha brought in Shulchan Aruch (Y.D. 92:5) that a drop of milk that falls on the outside of a pot of meat can assur the pot of meat. Therefore, as part of the kashering procedure for this kettle we will generally require that the hot water be drained.
One common exception to this rule is a pasteurizer/heat exchanger that was used for non-kosher grape juice and will now be used for kosher juice. In this situation, we do not require that the water that heated the grape juice be drained. This is based on the ruling of the Biur HaGra (Y.D. 103:16) that says that a bliah of wine is considered to always be nosain ta’am lifgam into water. Although wine itself requires bitul b’shaish into water, a bliah of wine is always batel in water. Since only bliahs of grape juice can leach through the walls, and not the actual grape juice itself, the water will always remain kosher. Any plitas that go back through the wall into the next product will be permissible.
Rav Belsky said that there is also another approach that we may take to be lenient. Grape juice that is batel b’shaish in water loses its status of wine and becomes permitted. The water used in the heat exchanger has no smell or coloring of grape juice. Its appearance is that of plain water. Although Chazal require us to be choshesh that this water received a bliah from the non-kosher grape juice, we can still see that this water has not changed into grape juice, and as such the plita of grape is surely batel.
Another exception to this rule is a pasteurizer/heat exchanger that was used for a drink that contained less than 10% dairy and will now be used for pareve. If we were to treat chalav stam as heter, then the bliah of dairy into the water would be a nat bar nat d’heteira, and the plita into the pareve product would be a nat bar nat bar nat and be permitted lechatchila.
Although we are machmir not to treat chalav stam as heter, in this situation we are still lenient, provided that the amount of dairy in the drink was less than 10%. This is because we see that the water exiting the heat exchanger has no smell or color of the dairy drink, but rather has the appearance of plain water. Although we must be choshesh that there was a bliah of dairy drink into this water, it clearly was less than one part in six (15%). Since the drink itself was only 10% dairy, and we do not say Chanan by chalav stam (as per the ruling of Pri Migadim 97:1), the plita of dairy would always be batel b’shishim in the water. Therefore, the water will always remain pareve. Another reason to be lenient in this case is because those who are lenient on chalav stam have tasted these drinks and have never detected any dairy flavor. Since this is a chidush, and a compilation of many sevaras, we may not extend this leniency to any other issurim.
- If the next product is a non-grape drink then any plita from this water will be pogem that drink as well and will therefore be permitted lechatchila (Shach 134:29). If the next product would be a kosher grape drink, then see Minchas Yitzchok II:36 that if we consider this to be a nat bar nat then this too would be permitted.
- Although this might be dependant in the machlokes between the Chavas Da’as and Pri Megadim as to whether we consider water cooked simultaneous to the milk to be a nat bar nat, here we have other reasons to be lenient.