At the feast of the Redemption through Moshiach, we will drink the “guarded wine” – wine that has been guarded in its grapes since Creation. Wine and grape juice need special guarding in order to be Kosher. It may not be touched by a non-Jew. (Many Kosher wine and grape juice companies cook the wine, and then if a non-Jew touches it, it is still Kosher. However, an opened bottle may still not be left unattended with a non-Jew around, because he may switch it with non-Kosher wine.) Guarding wine is even more crucial than guarding meat. Meat that was left unattended may not be eaten, but under certain conditions, if one knows what the meat looked like and recognizes it, it may be permitted (consult an Orthodox rabbi). Wine must be guarded because it can become non-Kosher by merely a touch.
(See talk of the Lubavitcher Rebbe King Moshiach Shlita, Vayechi 5752 (1991))