Avodah Zarah 31 - Touching the Wine

If Jewish wine was touched by an idolater, it becomes prohibited both for consumption and benefit. However, if it was only deposited in the idolater's house, it is prohibited to drink it, but benefit is allowed.

But why should this be? If we suspect that he touched it or exchanged it for his own, then it should be prohibited even for benefit. And we don't suspect this, then it should be permitted even to drink it! The answer is that the Jew has put his seal on the wine, and the idolater designated a corner where the wine was stored. The combination of the seal and the fear of being discovered makes it not worth his while to try to access the wine.

In general, the proper procedure for guarding the wine, for example, in the situation when the idolater is on the road with it and is unobserved, is to protect it with a double seal, which is hard to forge.

Art: Vladimir Egorovic Makovsky - At The Bottle