Question: May one crumble a clump of sugar or salt which has crystallized as a result of moisture on Shabbat?
Answer: In the previous Halacha we have established that one of the forbidden works on Shabbat is grinding. It is therefore forbidden to grind spices on Shabbat. We have also written that if one requires spices, such as black pepper, for one of the Shabbat meals, one may grind on Shabbat as long as two conditions are met: One must grind with the handle of a knife (and not with the edge of the knife that cuts) and this must be done within a bowl. However, to do so using a mortar and pestle (utensils designated for grinding) is forbidden even when this is being done for the Shabbat meals.
Let us now discuss the law regarding clumps of sugar or salt which sometimes crystallize as a result of moisture. May one crumble them on Shabbat or not?
Crumbling Salt or Sugar By Hand
It will certainly be permissible to crumble them by hand or using the handle of a knife and in a bowl, for we have written that it even permissible to grind black pepper using the handle of a knife and a bowl. Indeed, the Agur (Chapter 488 quoted by Maran Ha’Bet Yosef in Chapter 321, Section 1) writes that those who rule leniently regarding pepper rule leniently with regards to salt as well.
If Two Variations Are Necessary
Nevertheless, the Acharonim disagree whether two variations are necessary when one grinds salt or if one is sufficient. This means that it is certainly forbidden to grind salt in a grinder, however, there is room for discussion regarding whether it is similar to pepper in that it must be ground using the handle of a knife and a bowl or if it is permissible to grind salt using a regular knife (the cutting edge) and a bowl. The Zivchei Tzedek proves from the words of the Rashba (in his commentary on Shabbat 141a) that there is room for leniency and one variation is sufficient regarding salt. The Rashba (ibid.) explains the distinction between salt and other spices (see Chazon Ovadia-Shabbat, Volume 4, page 251).
Salt Nowadays Which Has Already Been Ground
On the other hand, all this applies to salt which was originally one block; however, our salt which was already fine and then clumped together once again as a result of moisture may be crushed on Shabbat without any variation whatsoever since “there is no grinding after grinding,” meaning that there is no prohibition to re-grind something which has already been ground using a knife just as it is permissible to cut very bread into very thin slices on Shabbat (since the flour has already been ground). Only when one uses a utensil designated specifically for grinding is this forbidden, for it will appear to others that one is grinding on Shabbat.
Summary: One may crumble a clump of sugar or salt which has crystallized on Shabbat for use during Shabbat. However, one may only do so using one’s hand, a knife, or a spoon and not with a utensil designated for grinding (Chazon Ovadia-Shabbat, Volume 4, page 251).