Halakhah sur Les Nombres 18:28

And it is practiced by males and females, by Israelites and by priests and by Levites. As even though the priests and the Levites take the tithe from [the Israelites], they are [still] obligated to tithe their [own] fruits on their lands. And it stands in the prohibition of unseparated fruit until they tithe them, as it is stated (Numbers 18:28), "So shall you give, also you." And the explanation upon it comes, "You" [is] the Levites; "also you" [is] to include the priests. But after they tithe them; if they want, they can eat the tithe themselves, or [they can] give it to a different priest. And this commandment of the tithe and also the commandment of the priestly tithe is only practiced in the Land of Israel by Torah writ - so did Rambam, may his memory be blessed, determine. And in the Order of Shoftim in the commandment of separating the great priestly tithe, we will elucidate more, with God's help, the differences that there are in the tithe and in the priestly tithe between the Land of Israel and Syria or (other places) outside the Land. If it is your desire to know, my son, learn it from there.

The commandment of the Levites to give a tithe from the tithe: That the Levites were commanded to separate a tithe from the tithe they take from Israel and that they give it to the priests, as it is stated (Numbers 18:26), "And to the Levites you shall speak, etc. and they shall give from it a gift to the Lord, a tithe from the tithe." And this is what is called 'terumat ma'aser' (literally, the gift of the tithe) in every place in the Gemara. They called it this expression in the way of the verse, which states, "a gift to the Lord." But the verse elucidates that he gives it to the priest, and as it states (Numbers 18:28), "and you shall give from it, the gift of the Lord, to Aharon the priest." And Scripture warns that he separate from the good and the choicest from the tithe, as it states (Numbers 18:29), "from all the fat that you sanctify from it." Moreover it is stated about this (Numbers 18:32), "You shall bear no sin upon it in separating its fat from it" - teaching that if he takes it out from the inferior [portion], there will be a sin upon them. And this matter is like the matter of a negative commandment that comes by way of deduction from a positive commandment, and therefore it is not to be counted among the negative commandments.

From the laws of the commandment - that which they, may their memory be blessed, said (Beitzah 13a) that a [Levite] who took sheaves as tithes, does not give sheaves to the priest from it, but he is fined to pound and winnow [it] and to give him a tithe of the tithe that is a tithe of grain, and he is not obligated to give a tithe of the straw [byproduct], after he pounded everything and winnowed [it], but if he first tithed the sheaths, and [then] pounded and winnowed [it], he must give [the priest] his portion in everything; that which they said (Mishnah Terumot 11:8) that only priestly tithes from the tithe with [at least] 1/64 of a log must he take to the priest, and so long as the priestly tithe is certain (not in doubt) and pure, [but] if it is less than this, he need not busy himself with taking it to the priest, but he rather throws it into the fire and burns it; that which they said (Mishnah Bikkurim 2:5) that the priestly tithe from the tithe can be separated from that which is not [close], as it is stated (Numbers 18:28-29), "From all the tithes [...] you shall gift," meaning to say even if you have a tithe in one country and [another] in another country, you may take one gift for all [of them], but nonetheless they, may their memory be blessed, said (Gittin 30a) that Torah scholars should only take it from [what is close]; and the rest of its details - are elucidated in Tractate Terumot, Ma'asrot, and in parts of Demai (see Mishneh Torah, Laws of Heave Offerings 1).

And also from the content of the commandment is that which they, may their memory be blessed, said (Rosh Hashanah 12b) that there is no obligation of priestly tithes and tithes until they come to a third [of their growth]. And so [too,] that which they said that the gleaning, the forgotten, the corner and the small grape strands of an Israelite (which are all reserved for the poor) are exempt from the priestly tithe and the tithes, even though he made a pile of them at home. And so [too,] that which they said (Mishneh Torah, Laws of Heave Offerings 3:4) that we do not take the tithe by weight or by number, but rather by estimation, since a measure is not stated about it in the Torah. And I have already written at the beginning of the commandment that a moderate eye separates one part in fifty by estimation. And he should not put the fruit into a pail or a basket the size of which is known, but he can take the priestly tithe in them [by filling] their half or their third. And it is permitted to separate the priestly tithe from that which is not adjacent; but nevertheless, Torah scholars do not do so. And so wrote Rambam, may his memory be blessed (Mishneh Torah, Laws of Heave Offerings 3:20). And that which they said (Kiddushin 41a) that a man can make an agent to separate the priestly tithe and the tithe, as it is stated (Numbers 18:28), "So shall you also separate the priestly tithe" - to include the agent who is likewise a member of the covenant (a Jew) - and many other laws in the Gemara about agency; that which they said (Mishneh Torah, Laws of Heave Offerings 6:1) that the priestly tithe is eaten by priests - whether adults or minors - themselves, their wives, their Canaanite slaves, and even their beasts; and many other laws in the Gemara about this, such as the wife that rebelled, the slave that escaped, the laws of divorce and engagement, and several similar to them; the laws of the priestly tithe concerning its nullification, about which the Sages, may their memory be blessed, gave a measure of [one part to] a hundred and one; and the rest of its many details are in Tractate Terumot, and some of its laws are scattered in many places of the Talmud.