Demai, Chapter One, Mishnah Two
As I stated in the Introduction to Tractate Demai, a person who has demai must take out second tithe and bring the second tithe to Jerusalem. Generally speaking second tithe would be redeemed for money, the money would be brought to Jerusalem and there used to buy food and drink. Our mishnah teaches that second tithe that is taken out from demai is treated differently from regular second tithe. This is because second tithe taken from demai is only doubtfully necessary and therefore the rules regarding it are slightly more lenient.
1) The [second tithe of] demai is not subject to [the rules of adding a] fifth.
2) It has no mandated time of removal.
3) It may be eaten by an onen.
4) It may be brought into Jerusalem and taken out again.
5) They may allow a small amount to be lost on the road.
6) One may give it to an am haaretz and consume its equivalent in Jerusalem.
7) [Second tithe money of demai] may be redeemed silver [coins] for [other] silver [coins], copper [coins] for [other] copper [coins], silver for copper, and copper for produce, provided that the produce is again redeemed for money, the words of Rabbi Meir.
a) But the sages say: the produce itself must be brought up and eaten in Jerusalem.
Section one: Normally, when one redeems second tithe, one adds a fifth of the value and brings that money to Jerusalem. However, when it comes to second tithe taken from demai, the one redeeming it does not need to add the extra fifth.
Section two: At the end of the fourth and seventh years of a sabbatical cycle a person must clear out all of the tithes from his house and give them to the appropriate party or destroy them. This does not apply to second tithe taken from demai.
Section three: An onen is a person whose close relative die (parent, sibling, spouse or child) but has not yet buried the dead. An onen cannot eat anything that is considered holy including second tithe, which is called holy. However, an onen can eat second tithe taken from demai, again because we are not even sure if this is really second tithe.
Section four: Once second tithe has been taken into Jerusalem, it is forbidden to take it out again. This rule does not apply to second tithe from demai.
Section five: If while traveling one has a small amount of second tithe from demai and it is not worth the trouble to take it to Jerusalem one may get rid of it. However, if one has a large quantity, one either must bring it to Jerusalem, or redeem it and then bring the money to Jerusalem. If it was regular second tithe, he couldnt even get rid of a small amount.
Section six: Generally speaking one cannot give second tithe to an am haaretz for fear that he will eat it while in a state of ritual impurity. However, he can give second tithe to an am haaretz as long as he later eats an equivalent amount of produce while in a state of ritual purity in Jerusalem. It seems that what he is actually doing is exchanging one amount of second tithe for another.
Section seven: It is forbidden to exchange coins that have been used to redeem second tithe for other coins. However, it is permitted to do so when the coins were used to redeem second tithe from demai.
There is another rule relevant in this section. Generally one cannot use second tithe coins to buy produce outside of Jerusalem. One who does so must take the actual produce and bring it to Jerusalem and eat it there. However, Rabbi Meir allows one to redeem this produce and bring it to Jerusalem, since the money used to buy the produce originally came from second tithe from demai. The other rabbis disagree and hold that this produce must be brought to Jerusalem, just as it is in a case of regular demai.