Maseches Ma'asros, Chapter 2, Mishnah 4. In these mishnayos we spell out the additional factors that can obligate a person to separate the full order of tithes, even though the usual event of completion of work has not yet taken place. In the previous mishnah we dealt with Shabbos; in the mishnah before us we will deal with the separation of Terumah Gedolah.
The three separations that fall upon the farmer:
Terumah Gedolah - to the kohen.
Ma'aser Rishon - to the Levi.
Ma'aser Sheni - to Jerusalem, or Ma'aser Ani to the poor, one or the other.
The essence of the mishnah is that at a certain point a person may become obligated in all the separations from the moment he separated Terumah Gedolah, even though he has not yet reached what we would call completion of work as it appears in the books.
What is the classic completion of work?
For produce intended for sale: from the moment the final stage of processing is done. The mishnah gives various examples: smoothing over the pile, or the oil and wine reaching the pit where they are to be collected, and skimming off the top layer at the place where the wine gathers. This is the end of production in the field, and from that point on one no longer eats a casual meal.
For produce intended for personal consumption: the window widens until the produce is brought home through the front door, or at the very least into the front courtyard.
The question before us is what the law is when, before the produce reached that boundary line, the person began separating Terumah Gedolah. The mishnah therefore opens with a case in which the separation of Terumah Gedolah is done in the field, before the processing has been completed: does this now obligate him in the separation of all the tithes, or not?
The words of the mishnah:
"Peiros she'teraman ad she'lo nigmerah melachtan" - produce from which Terumah Gedolah was separated while it was still in the field, before the final stage of processing. To illustrate: a kohen came and knocked on the door and said, "I see you are in the middle of threshing the wheat, but here I am now. Give me the wheat now, and you can finish the threshing afterwards." The question is whether it is permitted to eat from the rest of the wheat before tithing it, once he has already begun separating Terumah Gedolah from it.
Rabbi Eliezer forbids - "melachto nigmerah". Once a person has begun the process of separation, there is no way back: it is as though he declared that he has finished his work, and now he is obligated to tithe, and a casual meal is forbidden.
And the Sages permit - he is still in the very midst of production, and the fact that he separated Terumah Gedolah for the kohen before finishing his work in the field does not obligate him to tithe everything, and therefore a casual meal is permitted.
The exception of the basket of figs: the Sages permit in all of these cases except for a basket of figs. As we learned in the previous mishnayos, with figs the final stage is placing a covering - a palm leaf or the like - over the figs so that they will not dry out. Since this act is trivial and external to the preparation of the figs, this is an exception: if nothing remains to be done but this, and the person began separating Terumah Gedolah, there is no way back, and he must complete the separations before he eats. But apart from the figs, Rabbi Eliezer and the Sages disagree about one who separates Terumah Gedolah before the classic completion of work in the field.
The view of Rabbi Shimon: the mishnah goes on to say something somewhat complex: even regarding a basket of figs from which terumah was separated, where the Sages said that he must complete all the separations - Rabbi Shimon permits, and the Sages forbid. We have nothing to say about the double mention of the Sages; this is unusual in the Mishnah, and to the best of our knowledge there is no further lesson to be drawn from it.
Rabbi Shimon rejects entirely the notion that separating Terumah Gedolah ever forces the separation of the remaining tithes. His argument is this: a person is obligated to separate three things - Terumah Gedolah, maaser rishon and maaser sheni - and he separated only one of them; how can that one force the other two?
So in practice we have three positions before us. Rabbi Shimon says this even in a case where the processing of the produce in the field has been completed, so that the work is finished, but the person intends to bring the produce home for his own personal eating, in which case the window extends until he brings it home. Even in that case, if he stopped on his way home and separated Terumah Gedolah, Rabbi Shimon holds that it makes no difference: Terumah Gedolah does not force the other separations. In his view, on the way home after separating Terumah Gedolah a person may still eat from the produce as a casual snack, until he reaches the front of his house.
The three positions, built on two points: the first - separating Terumah Gedolah before the physical completion of the work; and the second - separating Terumah Gedolah after the physical completion of the work, but before the person has reached his home.
Rabbi Eliezer - is stringent: it makes no difference when, if he separated Terumah Gedolah, all the separations must be made at that same time.
The Sages - it depends: before the work is completed, Terumah Gedolah does not force the remaining tithes; after the work is completed - it does force them.
Rabbi Shimon - it never forces them. Separating Terumah Gedolah does not count at all among the things that now obligate the separation of the remaining tithes.
In summary: the halachah follows the Sages - before the work is completed, separating Terumah Gedolah does not obligate the other separations, whereas after the work is completed it certainly does obligate them, even if the person has not yet brought the produce into his home.