The Vinegar Industry the third in a series of articles regarding OU policy in the vinegar industry.
By: Rabbi Dovid Cohen

Kashering of vinegar equipment—general guidelines
1. Vinegar has a very strong odor which may linger in a tank long after the vinegar is removed. Must this smell be neutralized before the tank is kashered?
Answer: Yes.
2. If cold stam yayin or chametz is kovush in a tank for more than 24 hours, the tank can be kashered with milui v'irui or with irui kli rishon at 165° F. If almost any other issur had been kovush in the tank, the tank would require a full hag'alah. Does stam yayin vinegar have the same status as stam yayin regarding the above leniency?
Answer: Since vinegar is charif, one should l'chatchilah kasher the tank via irui kli rishon. If this is exceedingly difficult or impossible then the tank may be kashered via milui v'irui.
3. As a general rule, glass, cheress and all other materials absorb via kovush. One exception is that glass doesn't absorb stam yayin via kovush but cheress does. Is fiberglass treated like glass or like cheress? If fiberglass is treated like cheress and requires kashering, is milui v'irui effective (in the cases where milui v'irui is generally permitted)?
Answer: The treats fiberglass like cheress and therefore a fiberglass-lined tank would require kashering since cheress absorbs via kovush. Nonetheless, milui v'irui is effective just like milui v'irui is effective on all other forms of cheress.
4. How is milui v'irui performed?
Answer: Milui v'irui involves the following steps:
a. The tank must be cleaned and the cleaning must also remove any lingering odor of the non-kosher item from the tank.
b. The tank is filled to the top with water, and the water remains in the tank for at least 24 hours. Other liquids which are almost as fluid as water can be used instead of water as long as the liquid is not the same type of liquid as the issur was (e.g. wine, alcohol).
c. After 24 hours has elapsed, the water is discarded. Water used for milui v'irui of one tank may not be used for milui v'irui of another tank.
d. Steps "b" and "c" must be repeated two more times using fresh water. The repetitions do not have to be done on consecutive days and there can be a lapse of time between them.
e. Keeping the water in the tank for more than 24 hours at one filling does not allow one to leave it in for less than 24 hours at a subsequent filling.
5. The taste of wine or grape juice which is absorbed into the walls of a utensil has unique halachos. On the one hand, the absorbed taste of these items is always lifgam into any liquid other than wine or grape juice. On the other hand, the leniency of aino ben yomo doesn't apply to wine because wine improves with age. Do these differences also apply to stam yayin vinegar?
Answer: No. These halachos are not based on the fact that stam yayin is d'rabannan or a similar halachic rationale. Rather, the halachos are based on the physical properties of wine and grape juice and do not apply to vinegar.
6. The letter of the law is that non-kosher equipment which is asui l'hishtamesh b'shefah and aino ben yomo may be used for kosher production without kashering. Nonetheless, as a matter of policy the doesn't rely on this leniency except in cases of great need (see K-201). Would this leniency apply (in cases of sha'as hadchak) to equipment which is used exclusively for vinegar or another davar charif?
Answer: No. The equipment doesn't have the leniencies of an aino ben yomo because the vinegar (i.e. davar charif) which will be used in the equipment will reinvigorate the aino ben yomo flavor (see question ** of the ** edition of The Daf HaKashrus).