Avodah Zarah, Chapter Five, Mishnah 7. This mishnah covers several separate topics: accepting yayin nesech as wages, selling wine to a non-Jew, and the law of nitzuk chibur.
Yayin nesech as payment of wages:
The first topic deals with a Jew who receives payment from a non-Jew in the form of wine, which turns out to be yayin nesech. Since yayin nesech is forbidden to benefit from, the Jew cannot accept it as his wages: he may not drink it, and he may not sell it to someone else either. So what is he to do?
The essence of the mishnah is this: if the non-Jewish employer wants to pay his Jewish workers with yayin nesech, they may refuse and say, give us something else instead of the wine. This is not returning merchandise and it is not an exchange, but a rejection of that form of payment together with a request to be paid in another form. In other words, they are not trading yayin nesech for something of value; they are simply not accepting the yayin nesech in the first place.
But once the workers have accepted the payment in the form of wine, the wine becomes theirs, and from that moment on they may not trade it back to the non-Jew for something else, because such an exchange is deriving benefit from yayin nesech - selling the wine for something of value, which is forbidden.
In the words of the mishnah: "Umanin shel Yisrael she'shalach lahem oved kochavim kevesh shel yayin nesech bischaran" - the non-Jewish employer paid his Jewish workers with forbidden wine. "Mutar lomar lo: ten lanu es dameha" - they may reject this payment and demand the value of the wine, in money or in something worth money. "V'im mishenichnas lirshusan - assur" - once they have accepted the wine as payment and acquired it, they can no longer exchange it for anything of value, since that is deriving benefit from the wine, exactly like selling it. And just as they may not drink it, so they may not sell it. It emerges that once they have taken it as their wages, there is no way for them to derive any benefit from it at all, and all they can do is throw it into the sea.
One point deserves precision: the wording of the mishnah, "once it has entered their domain," could mislead, as though it were enough for the wine to have physically arrived in their area - so that if one day they found the barrel of wine sitting in their courtyard, it would already have entered their domain and they would be bound to it. That is not so: a person's courtyard acquires for him only to his advantage, and here the workers do not want the wine at all, so forcing it upon them physically does not make it theirs. The mishnah means that they accepted it as payment and made a kinyan on it, and from that point they may no longer return it or exchange it.
Selling wine to a non-Jew:
The next section of the mishnah is an entirely new topic: a Jew's kosher wine that is being sold to a non-Jew. The difficulty is that the moment the non-Jew takes hold of the wine it becomes yayin nesech, forbidden to benefit from, and it can no longer be sold. It follows that the sale must take place before the non-Jew takes hold of the wine, or at that very moment, but not afterward. How can this be arranged?
To answer this we need to understand the mechanism of a kinyan. A kinyan is a transfer of rights or a transfer of ownership, and it has two basic components:
Gemiras da'as: the agreement of both parties to transfer certain rights in exchange for a certain consideration.
The act of kinyan: the actual deed that brings about the transfer of rights.
So it is with kiddushin: the woman agrees to transfer her marital rights, and her husband-to-be agrees with her that her acceptance of the ring will render her betrothed and married to him - and when she takes the ring, the act of kinyan effects the transfer of rights. But if a man gives a ring to a woman who does not know that it is being given for the sake of marriage, there is no kiddushin here.
The same applies to buying and selling: the act that transfers ownership of merchandise is generally meshichah - physically taking hold of the item and drawing it toward oneself, and this rule is the same for a Jew and for a non-Jew. If a Jew sells a bottle of wine to a non-Jew, the wine becomes the non-Jew's at the moment he draws it toward himself. However, the act of acquisition is valid only if it was preceded by a meeting of minds in which the price was agreed upon, and both sides understand that taking the wine obligates payment of the agreed sum.
This yields two situations:
They set the price first: once the non-Jewish buyer has agreed to the price, then at the moment he takes the wine it becomes his and he becomes obligated to pay for it. The ownership and the obligation take effect at one and the same instant, so the Jew sold him kosher wine, and it became yayin nesech only at the moment when the obligation to pay had already been created.
There was no meeting of minds between them: the non-Jew who takes the wine may still ask what its price is and return it once he is told. Such taking is not an act of acquisition and does not bring the transaction into being; the wine does not become his, but it does become yayin nesech, since a non-Jew handled a Jew's wine. From this point on the Jew can no longer sell it to him, since it has become forbidden to derive benefit from it.
Here is the practical picture: the Jewish merchant has a large barrel of wine, and he measures out from it with a measuring vessel into the non-Jew's vessel. If the price was fixed in advance - a liter of wine for such and such a sum - and the non-Jew agreed, then from the moment he received the wine into his vessel and lifted it or moved it, the act of acquisition has taken place, the wine becomes his, and he must pay for it. This payment is permitted, because at the time he acquired it the wine was still kosher wine and not yayin nesech.
In the words of the Mishnah: if he set the price before measuring, the payment the Jewish merchant receives is permitted. If he measured before setting the price, the wine is already in the non-Jew's hands and has become yayin nesech, and there is no act of acquisition here, since there was no prior meeting of minds and no agreement on the price. And even if they agree on a price afterward, it is too late: the wine in question is already yayin nesech, and although it is a Jew's wine, what we have before us is a Jew's yayin nesech, and a Jew may not accept payment for it. Therefore the payment is forbidden.
Nitzuk Chibbur:
The next part of the Mishnah teaches an additional point. The Jewish merchant's practice is to pour the wine from his own vessel into the non-Jew's vessel by means of a funnel, so that the wine will not splash onto the floor: the wine is poured into the funnel, and from there into the tzelochis - the non-Jew's small jug. Now, if some wine remained at the bottom of the non-Jew's vessel from a previous use, that wine is the non-Jew's wine, and its status is yayin nesech.
Halachah discusses this on the basis of the principle called nitzuk chibbur. A nitzuk is an unbroken stream of liquid, and we say that a continuous stream joins the entire liquid into a single unit, so that it is all considered one mixture and one blend. And as we will see in the next Mishnah, even a single drop of yayin nesech mixed into kosher wine renders all of it forbidden. Therefore, according to those who hold that nitzuk chibbur - that an unbroken stream of liquid connects everything attached to that stream, or at least one stage of it - everything becomes forbidden: not only the wine in the non-Jew's vessel, but all the way up to the funnel and the funnel itself.
And if the funnel retains some of the liquid inside it - for example, when there is a lip at its bottom that holds back a little wine - then even after he has finished using it, forbidden liquid remains on the funnel. And if he then uses the funnel a second time to fill a bottle of a Jew's kosher wine, that wine too becomes forbidden, since a tiny quantity of forbidden wine that survived on the lip of the funnel has become mixed into it.
In the words of the Mishnah: "Natal es hamashpech u'madad l'toch tzelochiso shel oveid kochavim" - the Jewish merchant takes his funnel and measures and pours wine from his vessel into the funnel, and from the funnel into the non-Jew's vessel (a tzelochis is a sort of jug). If there were remnants of yayin nesech at the bottom of the non-Jew's vessel, the entire stream is connected and rises from the bottle up to the funnel, and everything becomes forbidden. "V'chazar u'madad l'toch tzelochiso shel Yisrael" - and if he then measured with that same funnel in order to fill the Jew's vessel, "im yeish bo kevesh yayin - asur": kevesh means a holding back, a lip at the bottom of the funnel that retains a little wine inside it. And if wine remained in it, even the wine poured into the Jew's vessel is forbidden, since a little of the wine that became forbidden on the funnel through the law of nitzuk chibbur has become mixed into it, having been connected to the drops of forbidden wine at the bottom of the non-Jew's vessel that was used earlier.
All this applies when there was a continuous stream. But "ha'me'areh mikeli likeli" - one who pours from one vessel into a separate vessel in a manner that involves no nitzuk, with no continuous stream but rather by splashing, so that there is no stream connecting the forbidden wine at one end to the source of the wine at the other end - "es she'irah mimenu - mutar": the wine that remained in the vessel from which he poured, the upper vessel, remains permitted, because there was no nitzuk here and no continuous stream creating a connection and a link.
"V'es she'irah l'socho - asur" - but all the wine in the lower vessel, the vessel into which the wine was poured, if it contained even a single drop of yayin nesech beforehand, becomes forbidden together with all the wine that mixed into it. For as we will see in the next Mishnah, yayin nesech renders forbidden in any amount whatsoever, even a single drop; and therefore, if the vessel is used a second time, and the first time it contained yayin nesech, the entire contents of that vessel are forbidden.
In summary: In this Mishnah we learned three matters: Jewish workers whose non-Jewish employer paid them with yayin nesech may refuse the payment and demand its monetary value instead, but once they have acquired it through a valid act of acquisition they may no longer exchange it, since it is forbidden to derive any benefit from it; in selling wine to a non-Jew everything depends on when the transaction became final in the minds of the parties - if he set the price before he measured out the wine, the money is permitted, because the wine became the non-Jew's while it was still fit; if he measured before setting the price, the wine became yayin nesech before it belonged to the non-Jew, and the money is forbidden; and regarding the law of nitzok, that an unbroken stream forms a connection - a continuous flow joins the entire liquid together, and therefore the funnel and the wine in it become forbidden, whereas one who pours from one vessel to another without a continuous stream, what he poured from is permitted and what he poured into is forbidden.
In the next Mishnah we will discuss the fact that yayin nesech prohibits a mixture in any amount at all, even a single drop that becomes mixed into kosher wine.