3,540. Second Tithe That Gets Mixed With Secular Produce

Hilchos Maaser Sheini and Neta Revai 6:13

If second tithe demai (doubtfully tithed produce) gets mixed with definite second tithe, the resulting mixture must be treated as the more stringent of them (which would be the definite second tithe).

Hilchos Maaser Sheini and Neta Revai 6:14

If second tithe produce gets mixed with secular produce, the resulting mixture must be eaten in ritual purity in Jerusalem or the second tithe must be redeemed. Accordingly, if such produce gets mixed in Jerusalem, even the smallest volume of the same species is rendered prohibited. Since it’s in Jerusalem, it is considered something that can be made permitted and it must be eaten in ritual purity.