Welcome to Maseches Maaser Sheni. Before we open the first Mishnah, let us introduce a few points about the nature of maaser sheni.
The order of the separations from the produce:
Terumah - a person separates Terumah from his produce and gives it to a kohen.
Maaser rishon - ten percent of what remains after the Terumah has been separated, and it is given to a Levi.
Maaser sheni - in the first, second, fourth and fifth years of the seven year shemittah cycle, which are the years of maaser sheni, one separates an additional ten percent from what remains after maaser rishon has been separated, and it is eaten in Jerusalem.
Redeeming maaser sheni:
A person is permitted to redeem his maaser sheni. One who redeems his own maaser sheni must add a fifth, which amounts to twenty five percent of the value of the maaser itself - that is, a fifth "milbar," calculated from the outside. After the redemption, the person brings the money up to Jerusalem, and there he must spend it on foods that are eaten in Jerusalem; it may also be used for offerings that are eaten in Jerusalem.
The difference between maaser rishon and maaser sheni:
Maaser rishon need not be eaten in a state of purity, and a person who is tamei may eat it. Maaser sheni, however, requires purity: anyone may eat it, and he need not be a kohen or a Levi, but he must be tahor at the time he eats it.
Let us turn to the first Mishnah (Maaser Sheni, Chapter 1, Mishnah 1):
"Maaser sheni ein mochrin oso" - because of its sanctity, it may not be sold. Even though one is permitted to redeem it, in which case the sanctity of the maaser sheni transfers to the coin, the produce itself remains in its sanctity. A person may not sell maaser sheni to his friend so that the friend should bring it up to Jerusalem and eat it as maaser sheni; selling maaser sheni in any way other than redemption is forbidden.
"V'ein memashk'nin oso" - it may not be used as collateral for a loan. Neither beis din nor the lender may take it as a pledge or security for a loan.
"V'ein machalifin oso" - it is forbidden to exchange it or trade it for something else. There are two explanations of this:
A person should not say: "I will give you my maaser sheni, and you will give me ordinary produce and bring it up to Jerusalem." The exchange need not be for money specifically; barter of goods is included in the prohibition as well, just as it may not be sold.
Even if both items are maaser sheni - one person has wine of maaser sheni and the other has oil of maaser sheni - they may not exchange them with one another, since this too is a form of commerce that may not be done with maaser sheni.
"V'lo shoklin k'negdo" - it may not be used as a weight. If a person knows that he has a litra of maaser sheni, he may not use it as a measure to weigh other things against it.
"V'lo yomar adam la'chavero bi'Yerushalayim: heilach yayin v'sen li shemen" - even in Jerusalem one may not make the exchange described above. Even when one person has wine and the other has oil and they wish to trade with each other, it may not be done - the exchange is forbidden even in Jerusalem.
"V'chen she'ar kol ha'peiros" - not only wine and oil, but all other types of produce as well. One way to understand this: the other fruits, apart from wine and oil, are obligated in maaser only rabbinically and not by Torah law, and the Mishnah teaches that even in those cases, where the obligation is only rabbinic, the very same halachah applies, and one may not make such an exchange with them.
"Aval nosnin zeh lazeh matanah chinam" - "But they may give one another a gift free of charge":
There is an opinion that "a gift is like a sale," meaning that giving a gift has the same status as selling, and according to this opinion it would be forbidden to give maaser sheni as a gift. The reasoning is that a person gives a gift only because he receives some benefit in return, even if this is never stated openly. A "matanah chinam," however, a completely free gift, is permitted. For example, when a person invites his friend to eat with him at his table, since it is accepted to host a person for a meal with no expectation of anything in return at all. Inviting a person to eat maaser sheni with you at your table is what is called a "gift free of charge," and in this manner they may give to one another.
In summary: in this lesson we clarified the place of maaser sheni in the order of the separations - after Terumah and maaser rishon, in the first, second, fourth and fifth years of the shemittah cycle; the option of redeeming it with the addition of a fifth calculated from the outside and bringing the money up to Jerusalem; and the requirement of purity when eating it, unlike maaser rishon. In the Mishnah we learned the restrictions that flow from the sanctity of maaser sheni: it may not be sold, it may not be used as collateral, it may not be exchanged, and it may not be used as a weight, and even in Jerusalem one may not exchange wine and oil or any of the other produce - but they may give one another a gift free of charge.