If on Shabbat a person wishes to serve a cluster of grapes for dessert, and he sees that several grapes are dried, spoiled, or otherwise undesirable, may he remove the grapes before serving the cluster?
One of the conditions for allowing Borer (separating) on Shabbat is that one may remove only the “Ochel” (desirable food) from the “Pesolet” (undesirable substance). It is forbidden on Shabbat to remove the “Pesolet” from the “Ochel.” Seemingly, then, it would be forbidden to remove the spoiled grapes from a cluster, since this would be removing the undesirable food from the desirable food.
However, Rabbi Moshe Halevi (Israel, 1961-2001), in his work Menuhat Ahaba, rules that one may remove the spoiled or unattractive grapes from a cluster on Shabbat. He notes that there are several factors which, taken altogether, provide a sufficient basis for ruling leniently in this regard. For one thing, Rabbenu Hananel (early 11th century) was of the opinion that the prohibition of Borer applies only to items that are detached from one another but mixed together. In his view, the prohibition does not apply to items which are attached together, as they constitute a single entity, and thus removing some items is not considered “separating.” Secondly, Rabbi Moshe Halevi cites authorities who claim that removing spoiled grapes from a cluster is considered “Derech Achila,” the normal, standard method of eating grapes, and Borer is allowed when it is done as part of the usual manner of eating.
It should be noted, however, that this Halacha refers only to removing grapes from the surface of the cluster. If a person sees undesirable grapes on the external layer of grapes, then he may remove them, but he should not go searching through the cluster for the rotten or unseemly grapes. Furthermore, removing unwanted grapes is allowed only just before serving the cluster. One may not remove the undesirable grapes in preparation for a dessert that he will be serving later on during Shabbat.
Summary: It is permissible to remove spoiled or otherwise unwanted grapes from a cluster on Shabbat, provided that this is done just prior to serving the cluster. However, one should not go searching through the cluster for unwanted grapes; he may remove unwanted grapes that he sees on the surface of the cluster, but should not specifically search for grapes that should be discarded.