The Gemara Avoda Zarah 33a teaches us that one can kasher a barrel that was used to store non-kosher wine with milui v’irui. This is accomplished by filling the barrel with water, letting it sit for at least 24 hours, emptying the barrel, and then repeating this process two more times. There is no need for the 3 days to be consecutive.
There are two explanations in the Rishonim as to why milui v’irui is effective:
- K’bolo kach polto – Some Rishonim1 understand that since the issur was absorbed through kevisha it can be purged with kevisha.
- Mafig Ta’am– Other Rishonim2 explain that milui v’irui does not cause the blios to be expelled, but rather weakens the taste of wine to the point that it can no longer assur.
Because we are machmir for both of these opinions, as we will see, milui v’irui has limited applications.
Here are some important halachos to keep in mind in determining whether milui v’irui is an appropriate method of kashering:
- Milui v’irui can only be used to kasher from non-kosher wine and heter such as chametz, kosher milk and kosher meat.3
- Chametz utensils can only be kashered with milui v’irui when they are aino ben yomo (Shach 135:33)
- Milui v’irui can only be used if the wine or heter were absorbed into the tank cold through kavisha.4
- Lichatchila we should not kasher holding tanks of wine vinegar which is considered a davar charif, with milui v’irui, but instead we should kasher with irui kli rishon. Where this is difficult, we may kasher with milui v’irui.5 Either way, Mishna Berura 451:120 says there must not remain a smell of vinegar.
Therefore, one must wash the tank well with soap until no odor remains. - Milui v’irui is effective in kashering cheres, glass and fiberglass.6
- One can use any mashke for milui v’irui, except one may not use wine when kashering from non-kosher wine.
- One cannot simply leave the water in the tank 72 hours. After the water is drained it cannot be used to do milui v’irui again, even for a different tank.7
- When kashering with milui v’irui one only needs to fill the tank to the highest level that the tank was ever filled to when it held issur.8
- In general whenever milui v’irui is an acceptable kashering, irui kli rishon and hagalah are also acceptable.
- Although we have noted that milui v’irui cannot be used for other issurim, it can be used as a snif b’shas hatzorech. For example, vegetable glycerin was produced on non-kosher equipment and then stored in a holding tank that could not withstand any heat. Rabbi Belsky allowed kashering this tank when it was an aino ben yomo with milui v’irui, because it was also a kli shemishtamshim bo b’shefa (See K-251).
- If one mistakenly did milui v’irui on a tank that held other issurim, bidieved the kosher product that is stored will not become assur, since it will always be an aino ben yomo. If one stored a kosher davar charif in this tank, there might still be reason to be lenient bidieved9 together with other tzirufim. The poskim should be consulted.
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1 The Rashba as explained by the Ran A.Z. 12b
2 The Ran A.Z. 12b
3 We cannot do milui v’irui on other issurim because we do not know if milui v’irui is sufficiently mafig those ta’amim.
4 We can only say k’bolo kach polto by milui v’irui if the bliah came in through kevisha
5 K-294
6 K-292: Although Rama 451:26 says the minhag is not to kasher glass that was kavush with chametz, the Mishna Berura 154 explains that this is only where a possibility exists that the glass was occasionally used with hot chametz. In industrial settings where this concern doesn’t exist, it is acceptable to kasher with milui v’irui.
7 K-304
8 The Rama 105:1 brings two opinions at to whether kavush will be mifafeiya above. The Shach says that the halacha follows the lenient opinion provided the issur is not known to be fatty. In general wine and chametz and milk are considered non-fatty. If one had fatty meat kavush in a tank then one would need to kasher the entire tank. Because this case is not common, it was omitted on top.
9 Chasam sofer Y.D. 110 says that even if an inappropriate kashering was done such as hagalah for a kli that needs libun, it still might weaken the issur enough that we will not say that a davar charif can be michalya ley lishvach.