It is common in many plants to have a product come out of an oven and go onto a belt. If the product is hot and non-kosher and it falls onto a cold belt, how must we kasher this belt?
First we must examine if this material is a davar lach or a davar gush. In regards to a hot davar lach that falls onto a cold surface, we follow the opinion of the Rema Y.D. 105:3. The Rema holds that we say tata gavar not only when a hot food item falls onto a cold food item, but also when a hot food item falls onto a cold kli. The kli cools the product and prevents the issur from entering more than a kdei klipa of the kli. Therefore, it is sufficient to kasher this belt with irui kli rishon.
If a large quantity of the davar lach was poured on the belt, such that it raised the temperature of the belt to the point where it no longer cools down the product, then we require that the belt be kashered with a prolonged irui. A mere irui kli rishon will no longer suffice.
If a davar gush fell on the belt then irui kli rishon is not sufficient. The Mishna Berura 451:114 brings the Mahari Viel 193 who says that kashering from a davar gush requires the use of an even miiluban (a super heated stone). The purpose of an even miluban is to boil the water against the surface of the belt. This is a higher level of kashering then irui kli rishon. The Achronim disagree as to whether this constitutes a full hagalah.
The reason we are more machmir by a davar gush, is because it does not have difanos mikariros (walls to cool it down). A davar lach, on the other hand, is surrounded by walls that cool it down quickly. This is also the opinion of the Maharshal. The Rema, however in Y.D. 94:7 does not differentiate between a davar lach and a davar gush. He holds that even a davar gush can no longer transfer ta’am after it is placed in a kli sheini. The Shach Y.D. 105:8, Taz Y.D. 105:4, and Magen Avrohom O.C. 318:45 are all choshesh for the Maharshal.
The Pri Megadim in A.A. 451:38 says that if only irui kli rishon was performed on such a belt, b’hefsed miruba we can be maikal. This is because we can rely on the opinion of the Rema that we say tata gavar even when a hot davar gush falls on a cold surface.
In summary:
- Davar lach, brief use – irui kli rishon
- Davar lach, prolonged use – prolonged irui
- Davar Gush – even miluban
- Davar Gush, bihefsed miruba – irui kli rishon
The exact definition of when an item is considered a davar gush or a davar lach is not so clear. Rabbi Schachter has ruled that the consistency of applesauce is still considered a davar lach.