Commentary for Avodah Zarah 61:13

This source describes a Jew who sends a substance with either a Samaritan or a non-Jew. Rashi explains that with brine the fear is that the non-Jew may switch it with his own brine that has non-kosher fish in it. Murias is also made of fish, but Rashi explains that it might have wine in it. In any case, if the Jew can tell that the wine, brine or murias has not been opened then he may drink it. But simply closing the cask is not sufficient.