The most important principle in the laws of Borer is the distinction between one who performs Borer in the manner of the melakha and one who is preparing food for immediate consumption. When okhel is separated from psolet in the manner of the melakha (derekh melakha), it is prohibited by Torah law, whereas one may take okhel from psolet as part of the act of eating (derekh akhila) even le-khatĥila.
For example, if peanuts are mixed together with shells, one does not need to eat the nuts with the shells. Rather, one may remove the nuts from the shells and eat them. This is not considered Borer; it is simply the way one eats, derekh akhila. This is not limited to one peanut either. One may remove a large quantity of peanuts from amongst the shells, place them in a bowl, and bring them to the table to eat, as this is the normal way to eat peanuts. One may also separate food for other people to eat. Therefore, one may remove many peanuts from their shells even in order to serve them to a friend.
There are three conditions that must be met in order for an act of separating to be deemed permissible as derekh akhila, rather than prohibited as derekh melakha:
1) One must pick out the okhel and not the psolet, because this is the way one normally eats. However, if one removes the psolet from the okhel, this is considered derekh melakha (see n. 10).
2) One must take the food with his hand the way one does when eating, and not with an implement designed for straining or separating (see section 7).
3) The preparation must take place just before consumption. If the separating is done long before the eating, this is considered derekh melakha (see section 6).
When these three conditions are met, it is clear that the act of separation is merely one of food preparation. But if even one condition is not met, then the actions are considered derekh melakha and violate a Torah prohibition.[1]
Let us return to the case of peanuts mixed together with shells. One may take the peanuts from the mixture and eat them only when all three conditions are met: 1) He removes the okhel (peanuts) from the psolet (shells); 2) he does so with his hands; 3) he does so for proximate consumption.
However, if one removes the shells from the mixture to prepare the peanuts for eating, since he is removing the psolet from the okhel, this is considered derekh melakha, and he has transgressed a Torah prohibition. Similarly, if he removes the peanuts in order to eat them much later, this is considered derekh melakha since it is not for proximate consumption, and he has transgressed a Torah prohibition. Additionally, if a gadget were devised to help separate peanuts from their shells, it would be forbidden to use it on Shabbat even for the purpose of immediately eating the nuts.
[1]. The three conditions are based on Shabbat 74a, according to the understanding of Rabbeinu Ĥananel. This is also the opinion of Rambam, Ramban, Ran, and many others, and it is how SA 319:1, 4 rules as well, as explained in MB’s introduction to §319. In practice, all Aĥaronim agree with this approach. However, some Rishonim disagree with two of the conditions: Tosafot on Shabbat understand Rashi to mean that one may separate for immediate consumption even with a sifter or strainer. Similarly, Rabbeinu Asher of Lunel maintains that if one wishes to eat immediately, he may separate the psolet from the okhel even using a utensil designed for that purpose. This is also recorded in his nephew’s work, Sefer Ha-hashlama.According to Rid and several other Rishonim, one may remove psolet from okhel for immediate consumption (Birkei Yosef mentions these opinions in Shiyurei Berakha.) Although the halakha does not follow them, these opinions can be combined with other mitigating factors to support leniency (BHL 319:4, s.v. “mi-tokh”). See Harĥavot.
