Before us is Mishnah 9 in the fourth chapter of Maseches Avodah Zarah - a fascinating mishnah from which some extremely important principles emerge. The first question the mishnah comes to answer is this: may a Jew work as a hired laborer for an idolater in his wine production plant?
Two issues stand for discussion here, and both of them are rabbinic:
Wages for working with something forbidden in benefit: There is a Torah prohibition against deriving monetary benefit from yayin nesech, and stam yeinam as well - wine whose nature is unknown - has the status of yayin nesech, so that any wine owned by a gentile falls under this restriction. The question is whether a person may work and earn wages performing tasks connected with that forbidden object: he is not buying, not selling and not drinking the yayin nesech, but only arranging crates or transporting them to market. The answer, in general, is no: a person may not accept payment for trading in something forbidden in benefit or for working with it, and assisting and supporting the process is forbidden rabbinically.
Rendering the produce of Eretz Yisrael impure: According to the tanna of our mishnah, there is a prohibition against causing tumah to produce grown in Eretz Yisrael in and of itself. This is not the accepted halachah - in halachah there is no prohibition against causing tumah to the produce of Eretz Yisrael as such, and although the practice is otherwise, when the food is fit to be eaten immediately, such as food bought in the market, it may be rendered impure even at the outset and directly by hand. Our mishnah, however, holds that even produce owned by a gentile, such as grapes in the winery of an idolater, if it comes from Eretz Yisrael, may not be rendered impure by rabbinic law.
In light of these two issues the question arises: is it permitted to take part in the work of the winery?
The mishnah says: "Dorchin im oved kochavim ba'gas" - one may tread the grapes and extract their juice together with the gentile in his winepress, that is, as a laborer in his employ. We must explain how the two questions are resolved.
As for the first question, receiving wages for working with something forbidden in benefit: our tanna holds like the tanna of the previous mishnah, that the wine coming out of the grapes does not become forbidden as yayin nesech until it collects in the pit. As long as it is up on the winepress, on the press itself, it does not yet have the status of wine, and it is permitted in benefit and even in drinking, as the previous mishnah stated. Consequently there is no receiving of wages for working with something forbidden in benefit, since until it enters the collection pit it is not forbidden in benefit.
As for the second question, transferring tumah to the produce of Eretz Yisrael, which in the view of the tanna is rabbinically forbidden: the case in the mishnah must be where the gentile already began treading the grapes before the Jew trod on them. For from the moment juice is squeezed out of the grapes, it is one of the seven liquids that make food susceptible to tumah. The mishnah's assumption is that the gentile's winepress is certainly impure, since every gentile is considered impure like a zav and anything that comes into contact with him becomes impure immediately. And once the first drop of juice emerged, the grapes and everything that became wet were already made susceptible to tumah. Therefore, if the gentile trod first, the Jew's treading adds no tumah at all - everything was already rendered impure by the earlier treading. The first stage of treading, however, the Jew would not be permitted to perform.
Two clarifications and the halachic ruling:
The first clarification: we distinguish between the juice that comes out of the grapes immediately, which has the status of wine with regard to making food susceptible to tumah, and its status with regard to yayin nesech, where it is not called wine until it flows into the pit below. This, however, is an early mishnah, and afterward the opinions reversed, and the halachah does not follow our mishnah on this point. We rule that the wine becomes yayin nesech and forbidden from the moment the juice flows and separates from the grape skins, and therefore even up on the winepress, a Jew who treads the grapes and causes the juice to come out is already dealing with yayin nesech, and he is receiving wages for it. Therefore, in practice it is rabbinically forbidden for a Jew to tread the gentile's grapes with him on the winepress.
The second clarification concerns causing tumah: in halachah we hold that there is no rabbinic prohibition against causing tumah to the produce of Eretz Yisrael. There is indeed a separate restriction regarding causing tumah to Terumah Gedolah, and likewise to challah and the like, but a gentile who owns land in Eretz Yisrael - his produce is not obligated in Terumah, and it is simply ordinary produce of Eretz Yisrael. And we rule in halachah that there is no restriction on rendering the produce of Eretz Yisrael impure, even directly by hand, as long as it is not subject to the obligations of tithes.
A Jew's winery operated in a state of tumah:
The next section of the mishnah discusses a case in which the owner and operator of the winery is not an idolater but a Jew, except that this Jew works in a state of tumah - his winepress is impure and it does not trouble him. From the perspective of the mishnah, which holds that one may not transfer tumah to the produce of Eretz Yisrael, he is treating halachah lightly and transgressing. And in truth, from the moment the grapes are owned by a Jew they are subject to the obligations of Terumah and tithes, and there is a prohibition against rendering tevel impure - produce from which tithes have not been separated - since ultimately the Terumah will reach the kohen in a state of tumah and will not be fit for him to eat. The Rishonim disagree as to whether rendering tevel impure is forbidden by Torah law or by rabbinic law, and in practical halachah we are lenient and permit causing tevel to become impure indirectly, but not directly by hand.
The question in the Mishnah, then, is whether one may participate together with a Jew who allows his wine to become tamei. To answer this, we need to distinguish between two separate matters:
"Lifnei iver lo sitein michshol" - the Torah prohibition of placing a stumbling block before the blind, which applies when without the assistance the sinner could not have committed the transgression at all.
Mesayei'a lidvar aveirah (assisting in a transgression) - a rabbinic prohibition, which applies when the assistance merely makes things easier for the sinner.
The classic illustration: the forbidden item lies on one side of a river, the person who wants to eat it stands on the other side, and the one giving assistance is in the middle. If he brings him the forbidden food, then without him the man could not have obtained it at all, and he violates "lifnei iver" by Torah law. But if the sinner is already standing on the same side of the river as the food, and he simply asks his friend to hand it to him, and had his friend refused he would have taken it himself - then the helper has only made things easier for him, and this is the rabbinic prohibition of assisting in a transgression.
It is worth knowing that this rabbinic prohibition of assisting in a transgression applies only at the time of the forbidden act itself. But before the act, when the assistance does not enable it to take place, and likewise after the forbidden act has been completely finished and a new act is being done with that same object - the restrictions of assisting in a transgression no longer apply.
In light of this we ask: may a Jew take part in the wine production process together with another Jew, when the employer is lax in halachah and causes his wine to become tamei? The Mishnah says: "Yisrael she'hu oseh b'tumah - lo dorchin" - another Jew may not join him in treading the grapes in the winepress. Even if the grapes were already tamei beforehand, he is participating in the very act of production, in pressing the wine out of the grapes, and that is the forbidden act itself, so he is assisting in a transgression. Even though the winery owner could have done it without him, the entire process of pressing the grapes is forbidden, and consequently the whole activity is restricted by rabbinic law as assisting in a transgression.
The Mishnah continues: "V'lo botzer imo" - he may not even join in harvesting the grapes and bringing them to the winepress, for this is the very same law: it is like serving the forbidden food on a silver platter, since he is enabling the transgression to come about by bringing the grapes to the place where they will be trodden and become tamei. The harvesting is part of the act of treading, and therefore it too falls under the rabbinic prohibition of assisting in a transgression.
What is permitted, however, is this: "Molichin imo chaviyos la'gas" - and "imo" does not necessarily mean together with him, but even on his behalf and in his name. One may transport the empty barrels, designated to hold the wine, to the winepress where they will be filled. And likewise "u'mevi'in imo min ha'gas" - one may transport the full barrels of wine from the winepress to the marketplace or to a storage facility. The principle that emerges: treading the grapes, and even preparing the winepress by gathering the grapes, are forbidden, because all of these are a single activity and one who takes part in them is assisting in the body of the act; but once the entire activity has been completed, doing something unconnected to it - such as bringing empty barrels or transporting barrels full of wine that has already become tamei - is not direct assistance, since the act has already been done, and the law of assisting in a transgression does not apply. One may therefore hire himself out to transport this wine that became tamei.
The law of the bakery:
The final part of the Mishnah closely parallels the second case, applying to a bakery the same laws that apply to a winery. In a bakery one takes flour, mixes it with water, and bakes bread. And even if the flour was fully tithed, a new obligation is created here: mixing the flour and water triggers the obligation of separating challah, the portion given to the kohen. Challah has the same status as Terumah, and it is forbidden to make it tamei. Therefore, if it is known that the baker uses vessels that are tamei, one who kneads the dough with him or shapes the loaves with him is participating in the very act of causing tumah to the challah, and he may not do so.
These are the words of the Mishnah: a nachtom, meaning a baker, "she'hu oseh b'tumah - lo lashin v'lo orchin imo". One may not take part in the kneading, that is, mixing the water into the flour and working it by hand, nor in the shaping, which is arranging and braiding the loaves. "Aval molich imo pas la'palter" - once all the work is finished, one may transport the loaves to the palter. The palter, according to Tosafos, is the one who buys the bread from the various bakers and then sells it in the marketplace - a sort of wholesaler or distributor. Bringing the baked loaves, even though they are tamei, is permitted and involves no rabbinic prohibition, since the bread is not forbidden in benefit, and the challah has already been separated elsewhere. One may therefore take responsibility for transporting these loaves that are tamei to the marketplace, since there is no restriction whatsoever on eating loaves that are tamei.
The approach of Rashi:
It is worth noting Rashi's approach, which is relevant to those learning the daf. Rashi explains that the palter is the one who does the actual baking: he buys the loaves while they are still dough, and he is the one who bakes them. The major practical difference is this question: the Mishnah forbade kneading and shaping - but is it permitted to bake the loaves in the bakery? According to Rashi the answer is yes, since baking is an activity separate from the act through which the loaves became tamei, namely the kneading and the shaping. According to Tosafos, however, it is forbidden, since making the bread - kneading, shaping and baking - is considered one single activity. Only once the loaves have been baked and completed may one be involved in transporting and selling them.
Summary: In this mishnah we learned two rabbinic restrictions - receiving wages for work involving something forbidden to derive benefit from, and causing tumah to the produce of Eretz Yisrael. We saw that in the view of the Tanna one may tread the grapes together with a gentile in his winepress, since the wine does not become forbidden until it flows into the pit, and since the grapes have already become susceptible to tumah and have been rendered tamei by the gentile's treading, whereas the halachah was decided otherwise on both points. We then clarified the distinction between "lifnei iver" - placing a stumbling block before the blind, which is a Torah prohibition, and assisting someone in committing a transgression, which is rabbinic, and we saw that the prohibition applies only at the moment of the act itself: one may not tread or harvest together with a Jew who works in a state of tumah, but one may carry barrels together with him to the winepress and bring them from there. So too in the bakery: one may not knead or shape the dough together with a baker who works in a state of tumah, but one may carry the bread together with him to the dealer, and regarding the baking itself Rashi and Tosafos disagree.