We come now to Mishnah 4 in the first chapter of Maseches Terumos, which introduces a new principle: based on a derivation from the verse, a person is not required to tithe his produce or to separate Terumah from it before the processing of that fruit has been completed. This principle is especially relevant to the production of grain, and likewise to the production of wine and oil.
The reason is straightforward: it is not proper to shortchange the kohen and hand him olives when the owner intends to produce oil. A great deal of labor is involved in turning olives into olive oil, and by giving over the olives as they are, the giver is cheating the kohen and saddling him with the work. Moreover, in oil production there is a significant economy of scale, and there is no real sense in preparing a small quantity of olive oil from a few olives. The same applies to making wine from grapes, and to completing the processing of grain by threshing and the like. Therefore, at the outset a person may not give the kohen his Terumah before he has finished processing the produce.
The novelty of the Mishnah - even after the fact:
Our Mishnah teaches that even after the fact, if a Yisrael gives his Terumah from the grapes at a time when he is producing wine, or from the olives at a time when he is producing olive oil, the separation is entirely ineffective. This is the main point of the Mishnah.
And it must be emphasized: in Mishnah 10 of this chapter we will learn that although the principle holds true, that one should not separate Terumah until the production process is complete, nevertheless after the fact, if a person separated grain before he finished threshing and winnowing and gave it to the kohen, the separation is effective and the grain has been rendered Terumah.
The distinction between grain and wine and oil:
We are forced to say that our Mishnah, which refers specifically to wine and oil, deals precisely with these crops, because with them the labor is so extensive and the advantage of scale is so significant relative to the starting point of olives and grapes. Therefore there is a rabbinic ruling here: if a person tries to separate grapes at a time when he is producing wine, or olives at a time when he is producing oil, and gives them as Terumah, by rabbinic law the separation is ineffective. In the Yerushalmi there is a dispute as to the reason for this, and several reasons are offered, but the point is one: this is a protection for the kohen, so that he not be shortchanged and not be treated unfairly.
The case the Mishnah is dealing with:
In fact the Mishnah is constructed in a more complex way. It discusses a case that is not spelled out in it: a person who has both olives and olive oil, and intends to keep both types together.
For if he were producing olives alone and had no intention of pressing them into oil, he would certainly be permitted to separate olives as they are and give them to the kohen. There is no requirement that the olive merchant press out a little oil for the kohen's benefit; if the processing is complete for him as olives, he may give olives. The same applies to the grape farmer: if he is keeping the grapes in order to eat them as they are or to turn them into raisins, we do not demand that he press them and make wine from them in order to give to the kohen; rather, he gives grapes.
The case in the Mishnah is where a person has grapes and also has wine, and he intends to leave half the crop as grapes and half as wine. Let us illustrate with numbers: he has fifty gallons of wine and fifty gallons of grapes, and this is his final intent. The measure of Terumah is one fiftieth, so he must give one gallon of wine and one gallon of grapes.
What would the law be if he took two gallons of raw grapes and said: "This is the Terumah for the grapes and for the wine"? That is, he is attempting to give grapes on behalf of wine. Do we say that at least with respect to the half that is grapes the separation is effective, and only with respect to the half that is wine it is ineffective, so that he will have to add and give more on behalf of the wine? Or perhaps we say that since he did it all together as a single portion, if the separation is ineffective for the wine, it is ineffective for the grapes as well?
The words of the Mishnah:
"Ein torimin zeisim al hashemen" - one may not separate olives as Terumah for olive oil and hand the olives to the kohen, and even after the fact the separation is not valid, by rabbinic law. "V'lo anavim al hayayin" - and likewise one may not separate grapes as Terumah for wine, for the same reason.
"V'im tarmu" - here the Mishnah returns to the case we presented: a person had fifty gallons of wine and fifty gallons of grapes, and he took two gallons of grapes and declared that one was for the wine and one was for the grapes. Beis Shammai and Beis Hillel disagree about this law:
"Beis Shammai omrim terumas atzman bahem" - at the very least, with regard to the grapes the Terumah takes effect. The portion separated for its own kind, the grapes, works, and those grapes are sanctified as Terumah for the grapes; only the portion corresponding to the wine will have to be separated again.
"U'Beis Hillel omrim ein terumah" - the Terumah does not take effect at all, since at that same moment he also separated for the wine. And since the Sages said that one does not take grapes for wine, the entire separation is void, and he must start over: to give one gallon for the fifty gallons of grapes and one gallon for the fifty gallons of wine.
In summary: in this Mishnah we learned that Terumah is not separated before the processing of the fruit has been completed, and with olives and grapes designated for oil and wine the Sages ruled that the separation does not work even after the fact - a protection for the kohen, so that he not be shortchanged. We noted the difference from Mishnah 10, where the separation does work after the fact, and the case of a person who designates part of his crop for grapes and part for wine: according to Beis Shammai the Terumah takes effect for its own kind, and according to Beis Hillel the entire separation is void.