In the previous Halacha we have discussed that one of the works prohibited on Shabbat by Torah law is grinding. It is therefore a Torah prohibition to grind spices, wheat, or barley on Shabbat.
Nevertheless, there is a very important point that we must point out, for many laws regarding the prohibition of grinding on Shabbat are contingent on it.
When we discussed the detailed laws of selecting on Shabbat, we explained that there are permissible methods of selecting on Shabbat when it is being done it the usual manner of eating not forbidden by Torah law. The same applies to the forbidden work of grinding on Shabbat in that there are several permissible methods of grinding on Shabbat, as we shall discuss.
The Permissible Method to Grind Pepper on Shabbat
The Gemara (Chullin 141a) states that Rava said that one who requires pepper (the same would apply to any spice including black pepper, allspice, paprika, and the like) on Shabbat may grind it on Shabbat as long as this is being done “with the handle of a knife and in a bowl.” This means that usually, when one grinds spices, one uses a pestle (a vessel used to hit and crush the spices) and a mortar (a hard bowl in which the spices are ground).
Rava therefore says that although may not grind spices on Shabbat using a mortar and pestle, one may grind spices on Shabbat using the handle of a knife and a bowl not designated for grinding. This is obviously only permitted when one does so for one of the Shabbat meals.
The Rambam (Chapter 21 of Hilchot Shabbat, Halacha 20) rules that grinding is forbidden on Shabbat unless two conditions are met: That one use the handle of a knife to grind (and not using a pestle or the cutting edge of the knife) and only in a bowl. This means that there must be two variations from the usual method of grinding and one variation does not suffice. Maran Ha’Shulchan Aruch (Chapter 321) rules likewise. Maran Rabbeinu Ovadia Yosef zt”l rules accordingly in his Chazon Ovadia-Shabbat, Volume 4, page 250.
Summary: Although grinding is forbidden on Shabbat, nevertheless, one may grind spices on Shabbat for the Shabbat meal when this is being done using the handle of a knife and within a regular bowl (and not one meant for grinding).