3,558. Using Up Most of a Coin's Sanctity

Hilchos Maaser Sheini and Neta Revai 8:13

The previous halacha (about transferring sanctity from one’s own money to a friend’s produce) applies when the friend is a learned person. This is because produce that is definitely second tithe may only be given to a learned person. If the produce was second tithe of doubtfully tithed produce (demai), then one may transfer sanctity with an unlearned person. One may transfer the sanctity of second tithe produce to the produce or the money of an unlearned person since we are not concerned that they might already be second tithe.

Hilchos Maaser Sheini and Neta Revai 8:14

Let’s say that someone puts aside a dinar of second tithe money whose sanctity he will transfer to the produce he eats. If he does this until less than a perutah of sanctified value remains, the coin is rendered secular. This is the case when it comes to demai. When it comes to definite second tithe, the dinar isn’t rendered secular until less than a perutah of sanctified value remains after a fifth has been added to it, i.e., less than four-fifths of a sanctified perutah remains.