The mitzva of separating terumot and ma’asrot falls to the owner of the produce. If someone else separated terumot and ma’asrot from another person’s produce without the owner’s consent, his act is void. However, a person may separate terumot and ma’asrot from his own produce on behalf of another person’s produce, even without receiving permission from him. Since he is taking the terumot and ma’asrot from his own produce, he also has the right to choose to whom they will be given (MT, Laws of Terumot 4:2).
When two people are partners in produce, either partner may separate terumot and ma’asrot from the produce without requesting permission from the other. If one of them separated without the other’s knowledge, and the second then came and separated again, the second separation is void, since the first partner’s separation had already made the produce permitted (MT, Laws of Terumot 4:8).
One who lacks the understanding needed to grasp the mitzva of terumot and ma’asrot and how it is performed cannot fulfill it. Therefore, a person lacking halakhic competence, such as one who regularly tears his clothing or destroys what is given to him; a person who is both deaf and mute and cannot read and learn; and minors may not separate terumot and ma’asrot. If they did so, their act is void. However, during the year before minors reach mitzva age – from age eleven for girls and age twelve for boys – if they separated terumot and ma’asrot and it later became clear that they understood the mitzva, then after the fact their separation is valid, since they have already reached the age at which their vows are halakhically binding (MT, Laws of Terumot 4:2, 5; below, 11, note 5).
Ideally, separation should be performed by someone who can recite the berakha and choose suitable produce for terumot and ma’asrot. Therefore, five categories of people should ideally not perform the separation. Three should not do so because of the berakha: one who cannot speak, because he cannot articulate the berakha; a deaf person, because one who recites a berakha should be able to hear it; and one who is unclothed, because one may not recite a berakha in that state. Two others should not perform the separation because there is a mitzva to choose good produce for terumot and ma’asrot, and it is assumed that they cannot do so properly: an intoxicated person and a blind person. After the fact, however, if any of these people performed the separation, it is valid and the produce may be eaten, because the mitzva is fulfilled even without a berakha and even if one separated inferior produce (Mishna, Terumot 1:6; MT, Laws of Terumot 4:4).
