Maaser Sheni, Chapter Five, Mishnah Six
There are two places in which the Torah discusses removing tithes from ones home. The first is Deuteronomy 14:28-29, Every third year you shall bring out the full tithe of your yield of that year, but leave it within your settlements.29 Then the Levite, who has no hereditary portion as you have, and the stranger, the fatherless, and the widow in your settlements shall come and eat their fill, so that the LORD your God may bless you in all the enterprises you undertake.
The second place is Deuteronomy 26:12-15, When you have set aside in full the tenth part of your yield — in the third year, the year of the tithe — and have given it to the Levite, the stranger, the fatherless, and the widow, that they may eat their fill in your settlements,
13 you shall declare before the LORD your God: “I have cleared out the consecrated portion from the house; and I have given it to the Levite, the stranger, the fatherless, and the widow, just as You commanded me; I have neither transgressed nor neglected any of Your commandments: 14 I have not eaten of it while in mourning, I have not cleared out any of it while I was unclean, and I have not deposited any of it with the dead. I have obeyed the LORD my God; I have done just as You commanded me. 15 Look down from Your holy abode, from heaven, and bless Your people Israel and the soil You have given us, a land flowing with milk and honey, as You swore to our fathers.”
The remainder of tractate Maaser Sheni deals with the laws concerning removing tithes from ones possession, which is supposed to occur, according to the rabbis, at the end of the third and sixth years of the sabbatical cycle, or at the beginning of the fourth and seventh years, depending on how you look at it.
1) On the eve of the first [others read last] festival-day of Pesah in the fourth and in the seventh [years of the sabbatical cycle] the removal was performed.
2) Terumah and the terumah of tithe were given to their owners, the first tithe was given to its owner, the tithe of the poor to its owner, and maaser sheni and first-fruits were removed in every place.
3) Rabbi Shimon says: first-fruits were given to the priests like terumah.
4) As for a cooked dish [with maaser sheni in it]:
a) Bet Shammai says: it must be removed.
b) But Bet Hillel say: lo, it may be considered as already removed.
Section one: Right before the last day of Pesah, after the third and sixth years have been completed, meaning at the beginning of the fourth and seventh years, one is commanded to remove any of the tithes that one may have kept lingering in ones home. This is how the rabbis understand Deuteronomy 14:28, Every three years.
Section two: Each agricultural gift is given to its rightful owner. Terumah and any terumah removed from tithes must be given to the priests, first tithe is given to the Levites, and poor tithe is given to the poor. Maaser Sheni and first fruits are special cases because normally these should be brought to Jerusalem and eaten there. There is no one to give them to. Therefore, they should be brought out and left to rot so that they can be totally removed from the world.
Section three: According to Rabbi Shimon first fruits are given to the priest. That is what the Torah means when it says, And the priest shall take the basket and place it before the altar (Deuteronomy 26:4). Rabbi Shimon also derives midrashically that first-fruits have the status of terumah. Since first-fruits are given to the priest, they do not need to be destroyed.
Section four: According to Bet Shammai, if there is a cooked dish that has maaser sheni produce in it, it must be removed just as maaser sheni itself must be removed.
Bet Hillel holds that since one cant see the maaser sheni, because it has blended in with the dish, it need not be removed.