If a Jew sells his produce to a non-Jew before gmar melakha, then by Torah law the produce is exempt from terumot and ma’asrot, since the stage that creates the obligation will be completed while it is in the non-Jew’s possession. The Sages, however, enacted that separation is still required. They did so because of ba’alei kisim – wealthy people who might try to avoid giving terumot and ma’asrot by selling their produce to a non-Jew before gmar melakha. To prevent this, the Sages established that even if the non-Jew completes the gathering, terumot and ma’asrot must still be separated. The produce is exempt only if the Jew sells it to the non-Jew while it is still on the trees, before it reaches onat ha-ma’asrot – that is, before it is fit to be eaten in pressing circumstances – and it remains in the non-Jew’s possession until after gmar melakha. In that case, it is exempt from terumot and ma’asrot (Menaḥot 67a; Rashi and R. Shimshon to Menaḥot 67a; MT, Laws of Terumot 1:13; Radvaz).
If a Jew and a non-Jew are partners in a field, terumot and ma’asrot must be separated from the produce. To avoid uncertainty over which produce belongs to the Jew’s share, which requires separation, and which belongs to the non-Jew’s exempt share, they should ideally divide the field in advance. The non-Jew’s portion will then be exempt, while the Jew’s portion will require separation. If they did not divide the field in advance, they should divide the harvested produce between them, and the Jew should separate terumot and ma’asrot from his share (SA YD 331:11; see the Herḥavot).
A non-Jew is not obligated to separate terumot and ma’asrot from produce that grew in his own field in Eretz Yisrael, and he cannot separate terumot and ma’asrot on behalf of a Jew. However, if he wishes, he may voluntarily separate from his own produce, and his separation takes effect (Mishna, Terumot 3:9; Yerushalmi, Terumot 3:5). Some maintain that this is a rabbinic enactment (MT, Laws of Terumot 4:15; SA YD 331:44). Others maintain that it is Torah law: just as a non-Jew can consecrate an offering, so too he can separate terumot and ma’asrot from produce he grew in Eretz Yisrael (Rashi and Tosafot; see Har Tzvi, OḤ 2:2).
