Bava Metzia 53 - Redeeming Second Tithe
For produce grown in Israel, second tithe should be separated and brought to Jerusalem - when the Temple is standing - and be eaten there. If it is too far to bring it to Jerusalem, or if the Temple is not standing, it should be redeemed for money.
If one wishes to redeem a small amount of second tithe, such as one grape, which is worth less than a prutah , he can’t do it for such small amount alone, but should add its sanctity to the money used for previous redemptions of larger amounts.
In a special case a small amount that was brought to Jerusalem - and then the walls of Jerusalem fell - cannot be redeemed.