Gemara

(Mishnah): One must give (Reishis ha'Gez) to the Kohen five Sela'im of Yehudah (this is ten of Galil).

Question: Rav and Shmuel taught that one must give one part in 60 of Gez, Terumah, and Pe'ah. (Rav obligates giving from a Maneh and a half, but a 60th part is less than a Sela!)

Answer (Rav and Shmuel): The Mishnah teaches that if a Yisrael has much shearings and wants to give them to many Kohanim, he must give to each Kohen five Sela'im.

Question (Mishnah): A generous separation of Terumah is one part in 40...

Do not say that Rav and Shmuel teach that mid'Oraisa, one must give one in 60, and mid'Rabanan, one should give one in 40. Shmuel himself taught that even one blade of wheat exempts the entire stack (mid'Oraisa)!

Answer: Mid'Oraisa, one blade exempts the entire stack. For Terumah mid'Oraisa (grain, wine and oil), Chachamim enacted that one should give one in 40. For what is liable mid'Rabanan, Chachamim enacted to give one in 60.

Pesachim 32b (Beraisa): If a Zar ate a k'Zayis of Terumah (b'Shogeg), he pays Keren v'Chomesh;

Aba Sha'ul says, he pays only if he ate the value of a Perutah.

The first Tana learns from "v'Ish Ki Yochal Kodesh bi'Shgagah." The Shi'ur of 'Achilah' (eating) is a k'Zayis. Aba Sha'ul's learns from "v'Nosan (la'Kohen Es ha'Kodesh)." The Shi'ur of 'Nesinah' (giving) is a Perutah.

Rishonim

Rambam (Hilchos Terumos 2:14): We give Terumah to a Kohen, whether it is Tahor or Tamei. He may benefit from burning Tamei Terumah. If it is oil, he may light it. If it is grain or similar things, he may fire an oven with it.

Rambam (3:1): The Torah gave no Shi'ur for Terumah Gedolah. L'Chatchilah, one gives only the Shi'ur that Chachamim fixed. Nowadays, it is is destined to burned, due to Tum'ah, so l'Chatchilah one may separate Mashehu.

Tosfos (Pesachim 32b DH v'Ein): Aba Sha'ul holds that 'Nesinah' is at least a Perutah. Chachamim disagree only because it says 'Achilah'. We hold that one piece of wheat exempts the entire stack (for Terumah), even though it says 'Nesinah'! We acquire with a Kli even though it is worth less than a Perutah, even though it says "he gave to his fellowman." A Get on Isurei Hana'ah is Kosher, even though it says "v'Nasan b'Yadah." We can answer that Nesinah of payment must be a Perutah, like returning theft, which must be at least a Perutah. Other places (that are not payment), even though it says Nesinah, do not require a Perutah. In Kerisus (6b), regarding putting Shemen ha'Mishchah on a Zar, R. Yehudah learns from Terumah to require a k'Zayis. He should be stringent to say that it is any amount, like we find regarding Zerikah, and putting blood and oil on the thumbs and toes of a Metzora, which is like anointing. This is not difficult for the opinion that argues with R. Yehudah and obligates for any amount.

Mishneh l'Melech (Hilchos Matanos Aniyim 6:7): A Tosefta (Pe'ah 4:2) says that we give Ma'aser Oni to an Oni no less than a half-Kav of wheat or a Kav of barley. There is no Shi'ur for Matanos Kehunah and Leviyah. Perhaps Tosfos asked based on this Tosefta. (Saying that one piece of wheat exempts the entire stack does not teach how much one gives to an Oni). It is not really any amount. The Rambam (Hilchos Matanos Aniyim 6:12) says that from the house, one gives a k'Zayis to each Oni. He holds that the Tosefta says 'any amount' to teach that one need not give the Shi'ur mentioned in the Mishnah (for giving in the field. This is like Chulin 137, in which Chachamim say 'any amount' to teach that it is less than the Shi'ur of R. Dosa. In Shabbos (25b DH Titen) Tosfos says that Nesinah must be a Shavah Perutah. In Kerisus (6b), we say that R. Yehudah learns from Stam Nesinah, which is a k'Zayis! One is lashed only for putting a k'Zayis of Levonah on Minchas Chotei (Menachos 59b)!

Tosfos Rid (Kidushin 58b DH Chitah): One piece of wheat exempts the entire stack. "Titen Lo" teaches that one must give a proper amount, like we say about Reishis ha'Gez! Surely, it is a Mitzvah to give a proper amount. If one separated only a drop, his Peros are not Tevel, but he does not fulfill the Mitzvah of giving.

Question (Mishneh l'Melech): Chachamim enacted that an average person separates one part in 50 for Terumah Gedolah. Surely, if this will not suffices to give a proper amount to a Kohen, one must separate more in order to fulfill the Mitzvah of giving. However, why did the Gemara challenge Rav, who said that one must take one part in 60 for Reishis ha'Gez? He can agree that if this will not suffice to give a proper amount, one must take more! Also, what forced the Gemara to answer that the Yisrael has much shearings, and wants to give to many Kohanim? We can say that the Shi'ur is always one part in 60. The verse discusses one who has more than a Shi'ur, and teaches that he should give a Shi'ur to each Kohen! Surely, one part in 60 is mid'Rabanan. We can say similarly about Terumah. What is the source to obligate separating enough to give a proper amount from a small stack? Perhaps "Titen Lo" applies when he has a lot to give, like regarding Reishis ha'Gez! Why did the Yerushalmi ask why Terumah was not listed among matters without a Shi'ur? According to the Tosfos Rid, it has a Shi'ur mid'Oraisa! Surely he overlooked the Tosefta that says that there is a Shi'ur only for Ma'aser Oni, but not for (Matanos) Kehunah and Leviyah.

Poskim

Shulchan Aruch (331:19): Nowadays, Terumah Gedolah is destined to burned, due to Tum'ah. The Shi'ur is any amount.

Rema: One gives it to any Kohen, whether a Chaver (Chacham) or ignoramus, even if he is not Meyuchas (of definite lineage), as long as he is Muchzak (established) to be a Kohen. He burns it. He may leave it (until he wants) to burn it to benefit from it while burning it. A Zar may not benefit from it while it burns unless also a Kohen benefits from it with him.

Taz (8): The Tur says that we are not concerned lest he benefit from it, even if he puts it in a Kli that is not repulsive. In the days of the Gemara, they were concerned lest he think that it is Tahor. Nowadays we are not concerned, for no one eats any Terumah. We are not concerned lest a Zar eat it, for every Kohen designates a special place for Terumah.

Note: The Kohen may benefit from it! If one might have thought that we are concerned lest a Yisrael benefit from it, putting it in a repulsive Kli will not deter this! It seems that the Tur means 'we are not concerned lest he eat it.'

Shach (30): Nowadays that Terumah is burned, we return to the Torah law that any amount exempts the entire stack.

Gra (35): Likewise, nowadays one may redeem Hekdesh for any amount. Even though the Tosefta and Yerushalmi say that if Peros became Tamei b'Ones, one separates one part in 60, that was at a time when other Terumah was eaten. However, why is this different than Chalah? Chalah of Keziv is burned, yet it has a Shi'ur! Sefer ha'Terumah asked this, and answered that those places were close to a place (Eretz Yisrael) where there is Taharah. Also, nowadays there is no Torah Terumah. The Yerushalmi says that nowadays Chalah is mid'Oraisa. However, this does not answer for the Rambam and Shulchan Aruch, for they rule that nowadays also Chalah is mid'Rabanan, yet it has a Shi'ur.

Gra (38): Even though it is a small amount and it is Tamei, one must give it to a Kohen. The Yerushalmi says that only in a case of (if one bought from an Am ha'Aretz, and he separated due to) Safek, he need not give it to a Kohen.

Noda bi'Yehudah (2 YD 201): Nowadays we take Mashehu of Terumah, give to Kohanim, and we let them save it until a time when they can profitably burn it (YD 331:19). Nowadays we take Mashehu of Chalah, and we do not give a significant amount to a Kohen. The Yisrael burns it himself. We don't tell the Yisrael to keep the Chalah until he has a proper amount to give, lest he stumble and use it to light his own oven). Regarding Terumah, we give also Terumas Ma'aser, which has a Shi'ur, therefore, one must give Terumah to the Kohen. The Shach (31) says that we are not concerned for Takalah regarding Terumah, for Kohanim know that no Terumah is eaten nowadays. In places where they separate two Chalos, one of them is eaten, so we do not allow Kohanim to keep around the Chalah that must be burned), lest he eat it. Since he may not store it, it is worthless for him to burn. This is according to the Mechaber. The Rema (322:5) holds that nowadays we do not eat any Chalah; we burn it. He primarily came to teach that there is no Shi'ur, but his reason also teaches why we burn it immediately.