In Maseches Avodah Zarah, chapter five, mishnah 3, we return to the topic we dealt with at the end of the previous chapter: when do we need to be concerned that a non-Jew touched wine that is supposed to be kosher, turning it into yayin nesech (or possible yayin nesech), which is forbidden to derive any benefit from. In the previous chapter we discussed cases where the wine was deposited in the non-Jew's domain and courtyard; here the wine belongs to a Jew, only that the non-Jew is nearby.
Mishnah 3 presents one case, and mishnah 4 will add two more cases of the same type.
The case in the mishnah:
"Oved kochavim shehayah ma'avir im Yisrael kadei yayin mimakom lemakom" - a Jew whose kosher wine is being transported from place to place hired a non-Jew to carry the jugs, and he himself accompanies the shipment (among other reasons, in order to watch over it). The question is when we need to be concerned that the non-Jew, who is an idol worshipper, secretly dipped his finger into the wine and performed a small libation.
"Im hayah b'chezkas mishtamer, mutar" - as long as the situation at every single moment is that the Jew has his eye on the jugs, the wine is permitted. 'Chazakah' means the presumed and existing state of affairs, and 'mishtamer' means being under the Jew's watchful eye. In other words: as long as the non-Jewish worker is worried throughout the entire journey that the Jew might see him at that very moment touching the wine, there is no room for concern.
The principle guiding these mishnayos:
Two forces pull at the mind of the idol worshipper:
Protecting his good name: he greatly values his reputation, and he would never do something for which he could be caught and portrayed as a cheat or as someone who acts improperly.
The desire to pour a libation: on the other hand, there is a real concern that a certain, not insignificant percentage of the population would indeed stick a finger into the wine and pour a tiny libation to idolatry, if only they could.
From here we get the common foundation of this mishnah and the ones that follow it: if the non-Jew had an opportunity to get away with it without being caught, we assume that he in fact did so, and the wine is forbidden. But where he would not have taken the risk, out of even a slight fear that at that very moment the Jew would notice him and confront him about what he was doing, we assume that he did not do it.
In our case the Jew is the employer, the non-Jew is carrying the jugs, and the Jew is present the entire time. But all of this applies specifically when there is some sort of cover on the vessel, even if it is not a sealed cover. Had the wine vessel been open, the non-Jew would not have been embarrassed, since he could stick his finger in and claim that something went wrong while moving the barrel, giving a reasonable excuse for what he did.
"Im hodia shehu maflig":
If the Jew informed the non-Jew that he is going away for a while ('maflig' means traveling a distance, becoming distant and separated), a window of time opens in which the non-Jew can pour a libation without being caught. The measure for this is "k'dei sheyishtom v'yistom v'yigov" - if the Jew was away from his wine long enough for the non-Jew to bore a hole in the vessel, gain access to a bit of wine, and then seal the hole up again.
This applies to a sealed vessel. And indeed that was the practice: amphora jars, tall and narrow, were sealed at the top with an almost permanent seal, such as a clay stopper, in order to protect the wine from oxidation. Therefore, if there was enough time for him to bore a hole in secret, insert his finger, reseal the jar and let the seal dry until it was no longer noticeable, we must suspect that he in fact did so, and the wine is forbidden.
Explanation of the Mishnah's wording:
"Yishtom" - to open. This word is rare in the Mishnah, and appears in the Chumash regarding Bilam: "shetum ha'ayin" - the open, perceiving eye. Here it refers to opening a small hole into the barrel.
"V'yistom" - sealing, to close and stop up.
"V'yagov" - to dry, from the words negev and magevet (towel), that it should dry so that it is no longer possible to detect that he tampered with the vessel.
The view of Rabban Shimon ben Gamliel:
Rabban Shimon ben Gamliel is lenient and allows a longer period of time, because in his opinion it is not enough for the non-Jew to bore a hole and insert his finger into it. According to him the measure is "k'dei sheyiftach v'yagof v'sagov":
"Sheyiftach" - that he remove the entire seal.
"V'yagof" - that he reseal it with a complete seal, from the word megufah, which is the name of the seal itself on a barrel of wine.
"V'sagov" - that the new seal dry completely and harden, until it is impossible to discern that it is new.
The reasoning of Rabban Shimon ben Gamliel: one who bores a hole in the upper part and covers it with a fresh layer of clay - even though from the outside nothing is noticeable, from the inside, beneath the outer seal, an observer will see that a change was made, since the hole that was plugged from above will be visible. Since it is possible to detect that he tampered with the vessel, he will not do it at all.
Everything depends, then, on the material from which the seal is made and on the amount of time needed for it to dry. And the point that emerges from all of this: whenever the act is liable to go undetected, we must suspect that it was in fact done.
In summary: our Mishnah deals with a Jew's wine being transported by a non-Jew. As long as the wine is in a state of chezkas mishtamer, under the Jew's eye, it is permitted, since the non-Jew is afraid of being caught. But if the Jew announced that he was setting sail, and enough time elapsed for the non-Jew to open, seal and dry - according to the Tanna Kamma, and according to Rabban Shimon ben Gamliel enough time to remove the entire seal, reseal it and let it dry - the wine is forbidden. The guiding principle: the non-Jew refrains from pouring a libation only out of fear of being caught, and whatever he is able to do in secret, we must assume he did.