Terumos, Chapter 2, Mishnah 6. We learned that the verse "bahareemchem es chelbo" teaches that a person separating his Terumah must take specifically from the finest quality. This is a mitzvah from the Torah, and therefore it is a full halachic requirement. We also said that one may separate from one species on behalf of another species. It emerges that there is a requirement to give Terumah from the better portion, but this means better in terms of quality, not a more prestigious category of food. Our Mishnah combines these two principles and clarifies several points.
Oil olives and pickling olives:
The Mishnah opens: "V'sorm'in zeisei shemen al zeisei kevesh" - one may separate Terumah from oil olives on behalf of pickling olives. We have before us two containers: in one are oily olives fit for pressing and producing olive oil, and in the second are olives ideally suited for pickling, which are not pressed at all because they are not so oily - these are 'zeisei kevesh', from the word for pickling. Although both types are olives, the superior one in terms of food quality is the oil olive, the one that would be pressed for olive oil.
One should not be confused here: this is not a case where these olives are about to be pressed for oil, because in such a case a separate problem would arise of separating from something that has not finished being processed and has not reached completion of its work. We are speaking of olives whose type can be pressed for oil, but which in practice will not be pressed. In such a case the correct thing is to take from the oil olives and not from the pickling olives designated for pickling, because the oily olives are of higher quality, and not the reverse.
"V'lo zeisei kevesh al zeisei shemen" - one does not separate Terumah from the pickling olives on behalf of the oil olives, because their quality is inferior and they are not included in "chelbo", the choicest.
Cooked wine and uncooked wine:
"V'yayin she'eino m'vushal al ham'vushal" - and uncooked wine on behalf of cooked wine. The same applies with two vessels: in vessel A there is cooked wine, wine that has already been boiled, and in vessel B there is wine that has not yet been cooked. One may take from vessel B on behalf of vessel A, since the higher quality product is the wine that was not cooked, and that is what is considered superior quality. From it one should take the Terumah.
It should be clarified: this is not referring to cooked wine in connection with the halachic considerations of cooked wine, whose status differs regarding the touch of a non-Jew and the like. In the times of Chazal it was common practice to cook wine extensively in order to reduce and sweeten it and so forth, and even so it is not considered of superior quality. Therefore, when a person has two types of wine before him, he must take from the wine that is not cooked. And in the words of the Mishnah: "V'lo min ham'vushal al she'eino m'vushal" - one may not separate from the cooked wine on behalf of the uncooked wine.
"Zeh hak'lal":
The Mishnah continues and states a general rule. However, as has already been emphasized many times and will be emphasized again, when the Mishnah uses the phrase "zeh hak'lal", it does not mean that there are no exceptions, but rather that this is the guiding rule, as will be explained below.
"Kol shehu kilayim bachaveiro - lo yisrom mizeh al zeh" - anything that is kilayim with its fellow, one may not separate Terumah from this on behalf of that. Two species that are considered kilayim and are forbidden to be sown together - the very fact that they are kilayim clearly teaches that they are different species and different categories. For this reason a person may not give Terumah from one on behalf of the other, "afilu min hayafeh al hara'ah" - even from the fine on behalf of the poor, even when what is separated is of the better quality.
For example, wheat and barley are kilayim with one another, and from this we learn that even though they are both grains and can be used in similar ways, they are different species, and one may not separate Terumah from the wheat on behalf of the barley or the reverse. Here the Mishnah comes to rule out a possible mistake: a person might think that if he has before him one container of barley and a second container of wheat, it would be better to take two portions of Terumah from the wheat, since the kohen will come out ahead - he will not receive barley but rather additional wheat, which is presumably what he wants, since wheat is preferable to barley. Says the Mishnah: it is not so. Wheat and barley are different species, and therefore one is obligated to take a portion of Terumah from each of the two containers separately - one for the wheat and one for the barley.
"V'chol she'eino kilayim ba'chaveiro":
This is the other side of the coin: two species that are not kilayim with one another, meaning that they are similar enough that they may be sown together, are considered a single species. We learned in Maseches Kilayim that oats and barley are considered one species, since they are not kilayim with each other. Therefore, someone who has oats in one container and barley in a second container may separate from one of them for both. Here too it is preferable to take from the finer produce when there is a clear difference in quality - and between barley and oats the matter is not decided - but the permission stands, since the absence of a prohibition of kilayim teaches that they are one species.
But we must understand: this is not a rigid rule but a guiding principle, meant to point the way in cases where the species resemble one another. There are many types of produce that carry no prohibition of kilayim when sown together, and nevertheless Terumah must be separated from each one on its own. For example, there is no problem of kilayim with any of the trees, except for grapevines in a vineyard, where the laws of kilayim certainly apply; but planting an olive tree in a vineyard involves no kilayim. The prohibition of kilai hakerem was stated only with regard to grain and vegetables, not with regard to trees.
The only Torah prohibition of kilayim with trees, outside the world of grapevines, is grafting one tree onto another: one may not take the trunk of one and the root of another and physically join them. Apart from that, trees may be planted alongside one another and they are not kilayim. And yet, even though one may plant an apple tree and a pear tree side by side and they are not kilayim with each other, it is certainly forbidden to tithe the apples for the pears or the reverse. It emerges that this rule before us is not entirely free of exceptions and qualifications.
In the words of the Mishnah: "V'chol she'eino kilayim ba'chaveiro - torem min hayafeh al hara'ah". Two species that are considered one species, such as two different varieties of rice or of wheat, may be separated from the better quality for the lesser. "V'lo min hara'ah al hayafeh" - one may not separate from the inferior variety of grain for the finer variety; someone who has two types of wheat before him should not take Terumah from the inferior type. "V'im taram min hara'ah al hayafeh - terumato terumah" - after the fact, if he separated from the inferior type for the finer, his separation is valid.
"Chutz min hazunin":
There is one exception: the zunin. The zunin is darnel, and it is worth noting that ArtScroll does not translate the word zunin here at all, even though in Maseches Kilayim it translated it as darnel. This plant is fascinating: it is known as "false wheat," it is almost indistinguishable from wheat, and it grows together with it. In ancient times an enormous percentage of the wheat crop was contaminated with it, and unlike wheat it does not do its eaters any good: it causes illness and nausea, and can lead to fainting and even to death by poisoning. In relatively small quantities it is psychoactive and produces a kind of drunkenness, the way drugs do. It therefore seems that many people in ancient times ate a bit of zunin in their food, whether deliberately or unknowingly, in both bread and beer, and became intoxicated from it.
A footnote in ArtScroll suggests that the word "zunin" comes from the root zanah, zonah - to turn aside and stray away, since this is a kind of degenerate wheat. The word darnel means to be drunk or intoxicated, and perhaps the idea is the same, since the plant turns the head of whoever eats it. Either way, zunin is no longer found in the Western world, although it still harms people and wheat crops in Africa and elsewhere.
And although zunin closely resembles wheat and is not kilayim with it when sown, since it is not human food one does not take from the inferior zunin for the wheat and give it to the kohen, because it is not food at all. This is the exception the Mishnah teaches: two species that are not kilayim, and nevertheless, one who takes from the inferior of the two, the zunin, for the wheat - his separation does not take effect halachically, since zunin is not food at all.
The kishut and the melafefon:
Finally: "HaKishut v'hamelafefon - min echad". Kishut is a cucumber; in modern Hebrew "kishu" is a zucchini, but that is certainly not correct, since the zucchini came from Italy at a late period and was not found in the days of Chazal. As for the melafefon, the Rambam here explains that it is an Egyptian cucumber, and ArtScroll translated it as gherkins, which are essentially pickles; since they are very similar, they are considered one species. Others held that the melafefon is a type of melon, and indeed there seem to be similarities between the way cucumbers grow and the way watermelons grow. Either way, the kishut - translated as cucumbers - and the melafefon, whether Egyptian cucumbers or melons, are considered a single species, and therefore Terumah may be separated from one for the other.
"Rabbi Yehudah omer: shnei minim" - Rabbi Yehudah disagrees and holds that the kishut and the melafefon are two different species, and one may not take Terumah from one for the other. But the halachah does not follow him: the halachah is that the kishut and the melafefon are one species, and one may take Terumah from one for the other.