The melakha of Toḥen (grinding) is prohibited on Yom Tov even if it is being done to prepare Yom Tov food. For example, grinding flour is prohibited, since this is usually done in quantities that are to last for a long time, and thus is considered melekhet avoda and forbidden on Yom Tov. Nevertheless, crushing spices is permitted on Yom Tov, since this is generally done in one’s kitchen for same-day use (Beitza 14a). No shinui is necessary (SA 504:1). Some maintain that it is proper to introduce a minor change, such as slightly tilting the pestle or the mortar containing the spices. This reminds the person doing the crushing that it is Yom Tov, and he will refrain from crushing extra for the upcoming week (Rema, ad loc.).
The permissibility of crushing spices is on condition that it is done with a household mortar – the kind that is generally used to prepare spices for the same day. In contrast, one may not grind peppercorns or the like using a small mill, since that utensil is generally used to prepare spices for lengthier periods of time (Beitza 23a; SA 504:1).
One may grate vegetables or cheese with a grater, since grating is usually done for same-day use. However, if for Yom Tov one needs to grate food which is sometimes grated to last for a number of days, a minor shinui should be introduced, such as turning the grater upside down, or grating over a tray instead of over a plate.[3]
Of course, everything permitted on Shabbat is permitted on Yom Tov. Therefore, one may crumble tea biscuits and matzot on Yom Tov. Since they are made of flour and have already been ground up, there is no prohibition to regrind them. Though on Shabbat it would be prohibited to use a utensil specifically designed for this purpose, such as a grater, so as not to appear to be doing something prohibited, on Yom Tov one may even use a grater (Rema 504:3; Peninei Halakha: Shabbat 12:1-2).
