What is the proper way to cut salad vegetables on Shabbat?
The Gemara states (listen to audio recording for precise citation) that a person who slices vegetables into thin pieces on Shabbat transgresses the Torah prohibition of "Tohen," grinding on Shabbat. The Rishonim (Medieval Halachic scholars) debate the question of to which vegetables the Gemara here refers. Most authorities (including the Rambam, Ramban, Raa, Ritba and Rosh) maintain that the Gemara speaks only of vegetables that cannot be eaten uncooked. When it comes to vegetables that are edible raw, however, Halacha imposes no restrictions regarding slicing on Shabbat. According to this view, it is entirely permissible to cut small pieces of many common salad vegetables such as lettuce, carrots and celery on Shabbat.
Rabbi Eliezer of Metz (France, 1115-1198), however, disagreed, and held that all vegetables fall under the Shabbat prohibition of "Tohen."
The Shulhan Aruch (Orah Haim 321:12; listen to audio recording for precise citation) codifies the prohibition against cutting vegetables into small pieces on Shabbat without drawing any distinction between different types of vegetables. He follows the stringent view of Rabbi Eliezer of Metz, who maintained that the prohibition of "Tohen" applies equally to all vegetables.
The common practice to allow cutting salad vegetables on Shabbat is based upon the ruling of the Rashba (Rabbi Shlomo Ben Aderet of Barcelona, 1235-1310) who allowed cutting vegetables just prior to the meal. In his view, the prohibition of "Tohen" does not apply to the preparation of food shortly before eating, and therefore it is permissible to cut vegetables just prior to the beginning of ones meal. Hence, women who wish to prepare a salad on Shabbat morning should ensure to begin doing so only at the time when their husbands leave the synagogue, shortly before they begin their meal.
Even so, it is preferable not to cut the vegetables into very small slices. Maran (author of the Shulhan Aruch) mentions this Halacha in his work Bet Yosef. Although it seems difficult to understand why this is necessary, one should preferably make a point not to cut the vegetables too fine on Shabbat, even when preparing the salad shortly before the meal.
Summary: It is permissible to cut vegetables on Shabbat shortly before eating, though preferably one should not cut the vegetables into very small pieces.
