Kashering Ben Yomo

One very practical application of ta’am lifgam is found in the middle of hilchos basar b’chalav. The Mechaber (Y.D. 95:4) says that if one places ash into a pot of hot water before dirty dishes are placed in it, then even if some dishes are milchig and some are fleishig, the pot and the dishes will remain kosher. This is because the ta’am of the ash combines with the ta’am of the fat and gives off a ta’am that is lifgam. This is the basis for the leniency to kasher kailim that are ben yomo, by using a davar hapogem (e.g. caustic).

Lichatchila one should only kasher kailim that are aino ben yomo. Even kashering a ben yomo kli in water that is 60 times the volume of its walls is only permitted bimakom dechak, because we are concerned that the kashering will not be done properly. This concern is even greater regarding kashering with a davar hapogem. However, b’shas hadchak we do allow such kasherings provided that the water is pagum ligamrei.

There are two approaches as to why kashering a ben yomo kli with a davar hapogem works:

  • The Pleisi (Y.D. 95:4) and the Minchas Yaakov (57:26) explain that when one cooks the davar hapogem, it gets absorbed into the kli and makes the bliyos of issur pagum. The kli is now like an aino ben yomo. One then kashers the kli a second time with plain water to remove the pagum bliyos of issur, the same way that we kasher an aino ben yomo kli.
  • The Chazon Ish (Y.D. 23:1) says that we do not have guidelines as to how to ensure that we were pogem the bliyos in a kli effectively. He suggests, that if the davar hapogem is boiled in the kli in a manner that would constitute a full kashering, we would say that all the bliyos in the pot is expelled into the water and become pagum. Whatever bliyos return into the pot are pagum m’tchilasom are not assur and do not require kashering.

We accept both of these approaches lechumra. Therefore, we require that the caustic cycle be roschim temperature, and we also require a second kashering with plain roschim water1. The lowest temperature that we can accept for roschim is above 190F. But lichatchila, we should try for boiling.

When kashering ben yomo silverware, it is common for mashgichim to be pogem the water with ammonia. Rav Belsky has said that if the pagum water remains clear (i.e. looks like plain ordinary water), there is room to be maikel, not to require a second kashering with plain water.

One situation where one may not be pogem a ben yomo kli is in regards to kashering a kli that needs libun. Since we are machmir to follow the Chazon Ish, we can only be pogem a kli that can be kashered with hagalah. Therefore, a spray dryer that requires kashering can never be used before waiting 24 hours, since it might require libun2, and we cannot be pogem a kli that needs libun. However, the spray dryer can be cleaned during the 24 hours, so long as it is cleaned with hot caustic and cold plain water (no plain hot water). If it will be cleaned during the 24 hours, it should be done in the presence of a mashgiach to make sure that it is done properly. Additionally, turning on a dry empty spray dryer during the 24 hours does not reset the clock, since this does not cause the bliyos to exit the walls of the kli and get reabsorbed into the kli.

In Summary:

  • Lichatchila one should only kasher an aino ben yomo
  • B’shaas hadchak one can kasher with 60 times the water or with caustic water.
  • In general we require two kasherings. One with caustic at roschim, followed by plain water roschim.
  • If the pogem water appears like plain water, there is room to be maikel to allow one kashering
  • One cannot be pogem a spray dryer. One must wait 24 hours.
  • However the spray dryer can be cleaned with hot caustic or cold water during the 24 hours
  • Heating up an empty spray dryer does not compromise the 24 hour wait
OU Kosher Staff