We are up to chapter 3 of Maseches Terumos, mishnah 1 - a wonderful mishnah dealing with someone who separated Terumah and afterwards discovered that the fruit or the liquid he separated was not what he thought it was at the time of the separation.
"HaToreim kishus v'nimtzeis marah":
A person separated Terumah from a cucumber, and it turned out that its taste was so bitter that it is barely edible. And likewise "avatiach v'nimtza saruach" - the fruit rotted on the inside and became soft and repulsive. Both of these cases are barely edible, and it is clear that they are not included in "chelbo" - the finest of the produce in the batch.
Even so, the mishnah rules: "Terumah" - by Torah law the Terumah takes effect, since it is still food. As we have learned, there is a mitzvah to separate from the choicest produce, but after the fact, one who separated from produce that was not of the best quality - his Terumah is valid Terumah. Here, though, the Sages plant their stake in the ground and say: "v'yachzor v'yitrom" - he must go back and separate a second time, taking a new cucumber or watermelon and giving it as Terumah in addition, and this is a rabbinic requirement.
Why is this case more severe than an ordinary case of Terumah that was not taken from the best produce? The Bartenura explains that here the one separating should have known in advance, and the matter borders on being intentional: he should have tasted what he was designating as Terumah before giving it. The simple understanding of this appears to be that cucumbers and watermelons commonly spoil, and certainly if 'avatiach' means an actual watermelon and not a melon in general. We have all had the experience of buying a watermelon, coming home and discovering that it is not fit to eat, and for that reason people prefer to buy pre-cut watermelon that can be checked in advance. Since he should have anticipated a significant chance that these foods would turn out to be spoiled, he should have tasted them.
And how can one taste them? In two ways:
Separating a small amount and checking it: to first separate only a small quantity and check the separated portion, in order to verify that it is of good quality.
Tasting before the work is completed: as long as the processing of the crop has not been completed, there is no obligation yet to separate Terumah, and it is permitted to take a casual taste from it.
These are two practical ways to get around the difficulty of checking the produce before designating it as Terumah. Either way, the Bartenura's approach is that the one separating should have known better and done better, and therefore the Sages obligate him to separate Terumah a second time.
"HaToreim chavis shel yayin v'nimtzeis shel chometz":
A person took a barrel of wine to serve as Terumah for the rest of the barrels, and it turned out that what he took was spoiled and had turned to vinegar. The case is one where a person has fifty barrels of wine, and he separates one of them thinking it is wine, and now it turns out that it is vinegar.
In the previous part of the mishnah we dealt with bitter cucumbers and spoiled watermelons, where the Terumah takes effect by Torah law and only rabbinically is he required to separate again, because he should have checked. But here, according to our Tanna, wine and vinegar are two different species. And if so, the separation is not effective even after the fact, since one does not take apples for oranges and one does not take vinegar for wine, and he must separate again. This is the approach of Rabbi Yehudah HaNasi, who arranged this mishnah, that wine and vinegar are two species. It is worth noting that there are those who disagree and hold that wine and vinegar are a single species, and after the fact the separation is effective, but that is not the approach of our mishnah.
And in such a case the mishnah distinguishes between three situations:
"Im yadua shehaysah shel chometz ad shelo tarmah - einah Terumah" - if it is known that the barrel that was separated on behalf of the other forty-nine was already vinegar at the moment of separation, this is not Terumah at all, since wine and vinegar are two different species, and the separation never begins to take effect. He must separate again.
"Im mishetarmah hechmitzah - harei zo Terumah" - if it is known with certainty that it turned to vinegar only after the separation, then at the moment of separation it was in fact wine, the spoilage happened afterward, and it is no fault of his. The Terumah takes effect.
"Im safek - Terumah, veyachzor veyisrom" - this is the fascinating and complicated case.
The doubtful case is where he separated the barrel, came back to check it a few weeks later, and found vinegar in place of the wine he thought he had separated - and he does not know whether it turned to vinegar before the separation or after it. Since separating Terumah is a Torah obligation, this is a doubt in Torah law. Therefore, on the one hand, that barrel of vinegar is treated with the laws of Terumah, since perhaps it really was separated while it was still wine; and on the other hand, "veyachzor veyisrom" - he must separate again from the remaining wine, since perhaps it was already vinegar at the time of separation and is not Terumah at all, and the other forty-nine barrels have still not been taken care of.
The result is that he holds two barrels: one of vinegar and one of wine, and both are treated with the laws of Terumah. Yet certainly both of them are not Terumah: either the first separation was valid and the second is not Terumah, or the first is not Terumah and the second is valid.
Let us note that we are not entering here into the side issue of separating tithes from these two halves - for if one of them is Terumah, the other is unconsecrated produce and is obligated in tithes and in second tithe. That is not the subject of this Mishnah. But there are further questions that touch on the status of the Terumah itself.
In practice, he must give both of them to a kohen, the vinegar and the wine together, since one of them is certainly Terumah, and a non-kohen may not drink from either one. However, since only one of them belongs to the kohen and the other remains his own in monetary terms, he is entitled to collect the difference from the kohen.
Let us say, for the sake of discussion, that one barrel is worth two dollars and the other three, so that in total he is handing the kohen five dollars' worth. How much may he collect from him? Up to three dollars. The reason: perhaps the kohen is entitled to only two dollars' worth, and the remainder is his own. And in monetary matters the rule is "HaMotzi meichaveiro alav hare'ayah" - one who seeks to extract money from another bears the burden of proof. Since the kohen cannot prove which of them is the genuine Terumah to which he has a claim, one is only obligated to give him the lower value, and the owner may collect the balance of the higher value from him.
The law of dimua in the two barrels:
Our Mishnah adds that because of the doubt there are additional halachos. First, the first barrel - the barrel of vinegar - does not create dimua on its own. Let us explain: in an ordinary mixture of a substance with the same substance, by Torah law we follow the majority. If fifty liters of forbidden vinegar fell into a large barrel of permitted vinegar, a simple majority suffices to nullify the prohibition: fifty-one permitted against fifty forbidden, and the entire mixture is permitted.
With Terumah, however, the Sages instituted the law of dimua, which requires one hundred against one. If fifty liters of Terumah fell into a barrel of vinegar, one needs one hundred times that amount - five thousand liters of non-Terumah vinegar - in order to permit the mixture. But this is a rabbinic requirement only. And here, since the first portion of vinegar is only doubtfully Terumah, this requirement does not apply, since a doubt in rabbinic law is decided leniently. Therefore, if the barrel of vinegar fell into a larger barrel of vinegar, a simple majority of permitted vinegar suffices to permit the entire mixture.
The same applies to the second Terumah, the wine: if it fell into a larger barrel of wine, the mixture is permitted provided that the majority of the mixture is permitted. There is no dimua problem with either one.
The law of the fifth in the two barrels:
The added fifth is a sort of penalty paid for eating Terumah unintentionally. A non-kohen who ate Terumah unintentionally pays the principal and adds a fifth to it. That is, one who drank four cups of Terumah wine first returns the four cups to the kohen in order to make it right, and adds a fifth cup as a sort of penalty - five cups in place of the four he drank. And if he did it intentionally, he does not add the fifth.
However, there is a difference between the four cups, which correspond to the principal, and the fifth cup, which corresponds to the fifth: the principal is indispensable for atonement, whereas the added fifth does not hold back the atonement after the fact. Therefore, someone who unwittingly drank the vinegar, which was the first Terumah, or the wine, which was the second Terumah, must repay what he drank, but he is not obligated to add the fifth, since the fifth is not indispensable for atonement and there is no certainty that he consumed Terumah at all (assuming he drank one of them and not both).
This is the meaning of the Mishnah: "HaRishonah ein hameduma bifnei atzmah" - the first quantity of Terumah, that is, the vinegar, does not create a mixture of meduma on its own and does not require one hundred parts against it. "V'ein chayav aleha chomesh" - and there is no obligation to add a fifth for someone who ate it unwittingly. "V'chen hasheniyah" - and the same applies to the second Terumah he separated, the wine: it carries no consequences of meduma, and there is no obligation of a fifth for someone who ate it unwittingly.
In summary: We learned that one who separates Terumah from a cucumber that turns out to be bitter, or a melon that turns out to be spoiled, has made a valid separation by Torah law, but by rabbinic law he separates again, because he should have tasted and checked beforehand. Regarding one who separates a barrel of wine that turns out to be vinegar, and according to the view of our Mishnah wine and vinegar are two distinct species, there are three cases: if it turned to vinegar before the separation, it is not Terumah; if it turned to vinegar afterward, it is Terumah; and in a case of doubt, it is treated as Terumah and he separates again. In the case of doubt he gives both barrels to the kohen and collects from him up to the value of the more expensive barrel, based on the rule that the burden of proof rests on the one who wishes to extract from another, and in both barrels there is no law of meduma and no obligation of a fifth.