Making saltwater on Shabbos is a complex issue. saltwater for the seder which is on Shabbos, should be prepared before Shabbos – to be safe. In case someone forgot to prepare it before Shabbos, it is Mutar to make saltwater provided it is less than 2 parts salt to one part water – but this is only if it is a small quantity. This may be an issue if people have large sedorim with many people. In that case, an easy eitzah is to add oil before mixing in the salt, the oil weakens the salt and makes it ‘unfit’ for pickling purposes.
Pickling vegetables or other foods which are typically pickled to preserve is assur on Shabbos. There are 2 few reasons in the Rishonim for this:
- The Rambam writes that this is Rabbinically forbidden because it resembles the Melacha of cooking. Cooking changes the status of food through heat. Pickling similarly changes the food. This is based on a halacha known as כבוש כמבושל, pickling is like cooking. Which may apply to baasar b’chalav as well…
- Other Rishonim explain that the issur of pickling is an extension on the prohibition of salting which is a derivative of the Melacha of Me’abed – tanning. As part of the tanning process, salt would be applied to the animal skins.
Rabbinically, it is forbidden to salt any food which is changed through salting, including raw meat and fish and most types of vegetables. Just as salting is forbidden since it preserves these foods, so too pickling is forbidden since it has a similar affect.
The Shulchan Aruch refers to both of these reasons.
Just the making of a large quantity of salt water is forbidden on Shabbos. Even if the liquid will not be used for pickling, but will be used for other foods, it remains forbidden. This is because it appears as though one was going to use it for pickling. The prohibition is not limited to making salty water. It applies to other liquids as well.
Based on this, the Shulchan Aruch (OC 321:2) rules that one may not prepare a large amount of salt water on Shabbos since this was done in the process of tanning hides. The Mishnah Berurah (321:11) defines a large amount as more than one needs for Shabbos. Since it is difficult to figure out exactly how much salt water one needs, the salt water should be prepared before Shabbos. If one forgot to prepare salt water before Shabbos, the Shulchan Aruch Harav (473:19) rules that one should make only a very small amount of salt water, which will only be enough for the dipping of the Karpas. For those who also have the custom to dip an egg in salt water, they may make enough to be used for the Karpas and the egg.