The Shabbat prohibition of "Borer," or "separating," which is included among the thirty-nine categories of Melacha (forbidden activity on Shabbat), forbids separating undesirable items from desirable items. When preparing food on Shabbat, for example, it is generally forbidden to separate the "Ochel" (edible food) from the "Pesolet" (inedible substance, such as peels or shells). Separating is permissible on Shabbat only if three conditions are met. First, one must remove the "Ochel" from the "Pesolet," and not vice-versa. This means that one takes the edible food away from the inedible substance, rather than taking the inedible material away from the food. Secondly, one may separate only by hand, and not with instruments such as sifters and the like. Finally, separating is allowed only "Le’altar," meaning, just before the food is needed. One may not separate in preparation for later in the day; it may be done only just before eating.
Is it permissible to separate food with a fork or other cutlery on Shabbat? Would this be considered separating with an instrument, which is forbidden on Shabbat, or do we view the fork as an extension of one’s hand, such that separating in this fashion is permissible?
Hacham Ovadia Yosef addresses this question in his work Halichot Olam, and rules that it is, in fact, permissible to separate food from inedible material with a fork or a spoon (assuming, of course, that the other two conditions for allowing "Borer" are also met). Halacha indeed views cutlery as an extension of the hand, and thus using a fork or a spoon to separate food qualifies as separating "by hand" which is permissible.
How long before the food is served may one separate? As mentioned, one of the conditions for allowing "Borer" is that one separates the food from the inedible material just before eating. How soon before eating must the separating be done to be permissible?
Hacham Ovadia Yosef rules that if a woman needs to separate food in preparation for Shabbat lunch, she may do so starting from the time when she figures her husband and guests have begun walking home from the synagogue. Once the people participating in the meal have begun making their way toward the house, it is permissible to separate food as needed to prepare for the meal. For example, if the woman knows that the services usually end at approximately 11:00, she may begin separating already from that point. Otherwise, if the separating is needed not for a formal meal, but rather for an informal snack and the like, "Borer" is allowed within an hour of when one expects to eat.
Summary: One may not separate desirable items from undesirable items on Shabbat unless three conditions are met: 1) he removes the edible food from the inedible material, and not vice versa; 2) he separates with his hand or with cutlery, and not with instruments such as sieves or sifters; 3) he does the separating just before the meal for which the food is needed. This means that the separating is done either one hour before the expected eating time, or once the people coming for the meal begin walking toward the house.
