Question: Is it correct that one may not put salt on cucumbers on Shabbat?
Answer: The root of this question lies in the fact that with regards to many Torah laws, we rule that “pickling is tantamount to cooking” meaning that a pickled food is considered like a cooked food. Thus, just as it is forbidden to cook on Shabbat, it is likewise forbidden to pickle foods on Shabbat either.
Although all of the works forbidden on Shabbat were works that took place in the Mishkan (Tabernacle) and there was no pickling done in the Mishkan whatsoever, our Sages (Shabbat 108b) nevertheless forbade pickling food items on Shabbat since “pickling is tantamount to cooking”.
Our Sages likewise prohibited doing anything which appears like pickling on Shabbat. For this reason, the Poskim, among them Maran Ha’Shulchan Aruch (Chapter 321, Section 3), rule that it forbidden to salt radishes on Shabbat since pickling radish was common in those times and by salting radish, one appears to be pickling it.
It is therefore forbidden to salt any vegetables which are usually pickled on Shabbat, including cucumbers, and to leave them in this state until they begin to “perspire” (ooze their natural juices). This therefore the basis for the above question and it would seem that it is forbidden to salt cucumbers on Shabbat and leave them like this for several minutes.
Although several modern-day Poskim rule accordingly, nevertheless, the prevalent custom is to act leniently in this regard and many people slice cucumbers and place salt on them, relying on the fact that cucumbers are generally salted only when they are whole. There is therefore no prohibition to do so when the cucumbers are sliced (see Shevut Yaakov, Volume 2, Chapter 12). Furthermore, when this is being done for the purpose of a meal, it is noticeable that one does not intend to actually pickle vegetables. There are several proofs to this lenient approach among the works of the Poskim (see Sefer Ma’aseh Ha’Shabbat, page 217). Thus, those who act leniently have on whom to rely.
Regarding a cut up vegetable salad commonly served at meals nowadays, however, there is certainly no concern in salting it since one’s actions show that one does not intend to salt the vegetables in order to pickle them (Halichot Olam, Volume 4, page 65). This is especially true since most of the vegetables in the salad, including the lettuce and tomatoes, are not commonly pickled at all.
Summary: It is permissible to put salt into a vegetable salad on Shabbat. This is especially true when oil is being placed onto the vegetables as well. If one wishes to salt cucumbers before one of the Shabbat meals, although there are those who rule stringently on this matter, those who act leniently and do so have on whom to rely.