Mishnah 8 returns to the case of two batches of produce - let us call them A and B - where Terumah is taken from B on behalf of both together. For example: fifty figs in A and fifty in B, one hundred in all. Two percent must be separated, that is, two figs for Terumah, and one may take one from A and one from B, or take both of them from B. This allowance applies only when A and B stand on the same level with regard to their Terumah obligations. The coming mishnayos present cases that clarify when taking from B on behalf of A is effective and when it is not - cases more subtle than those we have seen until now.
The guiding principle - gemar melachah (completion of processing):
A person is supposed to separate Terumah only from produce whose processing has been completed, what is called 'gemar melachah'. With grain - after threshing and winnowing, at the moment the finished pile is smoothed and leveled. With wine and oil - after the grapes have been trodden and the wine collected, or the olives crushed and the oil collected. This is the proper way: to wait until the processing is complete. The question is what the law is when he did not do so, or when he separates from produce part of which has been fully processed and part of which has not.
In our mishnah: B has already finished its processing, while A has not yet finished. May one separate Terumah from B, which is finished, on behalf of A, which is not?
"Ein tormin shemen al zeisim hanichtashim" - one may not separate Terumah from oil whose processing was completed in B on behalf of olives that have been crushed but not yet pressed, that is, olives in the middle of the process of extracting the oil, whose processing has not yet been completed.
It must be emphasized: we are speaking of olives in the middle of the process, and not of olives that are not destined to become oil at all - such as those that will be eaten raw or pickled. These olives are slated to undergo processing, and therefore have not yet reached gemar melachah, and one may not take the finished product of B - the completed oil - on behalf of A, which has not yet been finished.
"V'lo yayin al anavim hanidrachos" - and likewise one may not separate wine from B on behalf of grapes in A that still need to be trodden, or whose treading has not been completed, and whose juice has not been fully extracted from them.
"V'im taram - terumah" - and if he transgressed and separated, his Terumah takes effect: the two units he took from B are Terumah in every respect. However, the Sages penalized him - they imposed a penalty in order to prevent separating Terumah from produce whose processing has not been completed, and they require him to separate again after he finishes processing the grapes or the olives.
By Torah law the separation is effective: one who separates wine on behalf of grapes, or oil on behalf of olives - his Terumah is valid Terumah, and there is no problem with it. The kohen also loses nothing, since he received the oil or the wine just as he would want. The concern is that the next time he may do the reverse, separating from the unfinished produce on behalf of the finished produce, and thereby rob the kohen. For this reason he was penalized to separate a second time.
The difference between the first separation and the second:
Take note: the first separation is Terumah by Torah law, while the second is considered Terumah only by rabbinic law. Therefore, in the first separation - where A had unfinished produce and B had finished produce - the two units that were taken are full-fledged Terumah, and the following consequences result:
"Medama'as bifnei atzmah" - the oil or wine that was taken creates dimua. Normally, in a mixture of a substance with its own kind - olive oil in olive oil or wine in wine - we follow the majority; but regarding Terumah a special rule of dimua was stated, requiring more than ninety-nine parts (and some say one hundred) of chullin against the Terumah in order to nullify its status. This stringency applies to the first portion, which is Terumah by Torah law.
"V'chayavin aleha chomesh" - a non-kohen who eats Terumah unintentionally returns the Terumah, and for every four units he ate by mistake he adds a fifth unit, as a kind of penalty. If he drank four cups of wine without realizing that they were Terumah - he must return five cups. This obligation applies to Terumah of Torah law, and therefore applies to the first portion.
"Aval lo sheniyah" - the second portion, the penalty portion that he is obligated to separate from the wine or oil after he has finished processing the grapes or olives mentioned in the first clause, is not Terumah by Torah law but only by rabbinic law. For that reason it does not require ninety-nine parts against it in order to be nullified, and there is no obligation of an added fifth: one who ate it unintentionally pays only the principal, and does not add a fifth.
The Tiferes Yisrael's addition:
The Tiferes Yisrael adds an important point: since by Torah law this second Terumah is not Terumah at all, but completely ordinary produce that merely carries the name Terumah, the various tithes were never separated from it. Genuine Terumah is exempt from tithes - maaser, maaser sheni and the like - whereas this is not. Therefore, even though he gives it to a kohen and the kohen eats it as Terumah in a state of purity, the kohen must first separate from it the tithes that must be separated from any ordinary produce.