1) ONE OR TWO SEALS
OPINIONS: Rav states that if a Jew seals milk, meat, wine, or Techeles in a package with only a single seal and he sends it with a Nochri courier, then the item becomes prohibited (see Rashi to 39b, DH Asurin, Insights to Avodah Zarah 31:1). However, if a Jew sends Chiltis (a type of sharp-tasting fruit)), fish fat or brine, bread, or cheese in a package with only one seal, then the item remains permitted.
What is the reasoning behind Rav's ruling?
(a) RASHI explains that since meat and Techeles are very expensive items, we are concerned that the Nochri will exert the effort to remove the seal and take the meat and Techeles for himself, and exchange the items for items of lesser value. Similarly, since the Nochri uses wine for libations to his idol, we are concerned that he will remove the seal, pour the wine to his Avodah Zarah, and then replace the wine and re-seal the package. Therefore, these items require two seals. (The Gemara itself discusses the requirement of two seals for milk.)
Rashi implies that the second set of items that Rav mentions require only one seal because they are less expensive, and we are not concerned that the Nochri will remove the seal in order to take the items and then attempt to forge the seal.
TOSFOS (39a, DH Amar) quotes RABEINU EFRAIM BAR DAVID who disagrees with Rashi. He asks that fish fat is certainly more valuable than wine, and thus it should also require two seals.
Tosfos quotes RABEINU YEHUDAH who answers that fish fat is not always more valuable than wine. There are many places where wine is more valuable than fish fat. The Gemara earlier (34b) explicitly states that there are some places where wine costs four times the price of fish fat. He provides additional support for Rashi's explanation from the Gemara later which states that we are less stringent with a package of cheese and bread (which are much less costly), since the Nochri will not bother to attempt to forge the seal.
It is interesting to note that Rabeinu Efraim understands that Rashi's reason for requiring two seals for wine is because wine is expensive, like meat and Techeles. The TUR (YD 118), however, clearly understands that Rashi is giving a separate reason for why wine requires two seals. Rashi is saying that since the Nochrim use wine for their idol-worship, they will take whatever wine they can get, and therefore it requires two seals. According to this understanding of Rashi, Rabeinu Efraim's question on Rashi is not a question at all.
(b) RABEINU EFRAIM explains that the reason the items in the first set require two seals is because of the nature of the potential prohibition of these objects. Meat, wine, and Techeles that are handled by Nochrim become inherently forbidden to be used by a Jew, while the items in the second set become forbidden only because of what the Nochri might mix into them. This is also the opinion of the RITVA and the RAN, who quotes this reason directly from the Yerushalmi.
The Ritva and Ran address the fact that this reason does not seem to apply to all the items. Milk of Nochrim is not forbidden because of any inherent prohibition, but rather because of the suspicion that the Nochri added milk from a non-kosher animal. The Ritva adds that this is the very reason why the Gemara itself (39b) asks why milk is any different than cheese, which does not require two seals. The Gemara indeed answers that milk does not require two seals, and Rav was referring not to milk, but to a piece of fish that has no sign that it is kosher. (The Tur's text of the Gemara apparently replaces Chiltis in the second list with milk. The RIF has yet a third version of the Gemara's text, which adds milk to the second list and retains Chiltis, making the second list comprised of five items.)
Why, though, does bread not require two seals? The bread of Nochrim was prohibited by the Rabanan with an inherent prohibition, and not because of anything that the Nochri might have added to it! The Ran and Ritva answer that because the prohibition is only mid'Rabanan, the Rabanan did not require that it be protected with more than one seal. Wine, on the other hand, is the opposite; although "Stam Yayin" of Nochrim is prohibited due to an Isur d'Rabanan, the Ritva explains that because there is an Asmachta in the Torah for the prohibition (29b), the Isur is treated more stringently than the Isur of bread of Nochrim.
(c) The Tur (ibid.) quotes the RASHBA who explains that the items in the first list require two seals because they involve potential Torah prohibitions (milk of a gentile might contain milk from a non-kosher animal, the meat of a gentile might be that of a non-kosher animal, the wine of a gentile might have been used for idolatry, and the blue dye that a gentile might exchange for real Techeles will invalidate a person's Tzitzis), while the second list contains items that might be prohibited only mid'Rabanan. The BEIS YOSEF (ibid.) states that this also seems to be the opinion of the RAMBAM (Hilchos Ma'achalos Asuros 13:10). (Although wine and bread seem to be on the wrong lists, we can use the explanation of the Ritva regarding Stam Yayin and bread to understand the Rashba's opinion.) (Y. MONTROSE)
2) HALACHAH: DRINKING THE MILK OF NOCHRIM
OPINIONS: The Gemara records a Beraisa which says that a Jew may sit at the side of the herd of animals of a Nochri and partake of milk that the Nochri brings to him from his herd. The Gemara inquires regarding the details of the case. If the case is one in which the Nochri has no non-kosher animals in his herd, then it is obvious that the Jew may drink the milk! If, on the other hand, the Nochri has non-kosher animals in his herd, then why is the milk permitted? The Gemara concludes that the case is one in which there are non-kosher animals in the Nochri's herd, and the Jew cannot see the Nochri from his position when he sits down. The Beraisa is teaching that the milk brought to the Jew is still permitted, since the Nochri is afraid to attempt to trick the Jew (by bringing him non-kosher milk) when the Jew might easily reveal the Nochri's deceitfulness.
What, though, is the Halachah in the Gemara's first possibility, when the Nochri does not have any non-kosher animals in his herd? May the Jew drink the Nochri's milk even without having supervised the milking?
(a) The MORDECHAI (#826) quotes an opinion that says that it is permitted to drink the milk of a Nochri when there are no non-kosher animals in his herd, since the Gemara assumes in its question that it is obvious that the Nochri's milk is permitted when there are no non-kosher animals in his herd. This implies that a Nochri farmer who owns only kosher animals does not need to be supervised in order for his milk to be permitted.
(b) The Mordechai himself says that this opinion is mistaken. If the Gemara means that no supervision is required, then it should ask why does the Beraisa mention that the Jew is sitting next to the herd? If no supervision is required, then the Beraisa would not have mentioned that the Jew is sitting next to the herd!
Rather, some degree of supervision is necessary for the milk to be permitted. He quotes RABEINU BINYAMIN from CANTERBURY who says that the Gemara means to say that if there is no non-kosher animal in the herd, then it certainly suffices for the Jew to be sitting on the side watching, even if he does not see all of the milking.
The Mordechai then quotes RABEINU PERETZ who rules that a Jew certainly must be present at the beginning of the milking process, even when there is no non-kosher animal in the herd, in order to ensure that the Nochri does not begin the milking process with some leftover, non-kosher milk in his pail.
This also seems to be the opinion of the SHACH (YD 115:5). The SHULCHAN ARUCH (YD 115:1) says that if the Nochri is milking the animal in his house and the Jew is sitting outside, the milk is still permitted as long as it is known that the Nochri does not have any non-kosher animals. The REMA adds that l'Chatchilah the Jew should be present at the beginning of the milking to ensure that there is no non-kosher milk in the pail at the start of the milking. The Shach comments that the Rema says his comment even in the case where the Nochri has no non-kosher animals in his herd. This is clear from the Rema's commentary on the Tur, DARCHEI MOSHE (YD 115:1), where he explicitly states this in the name of the MAHARI and the HAGAHOS MAIMONIYOS.
The MATEH YONASAN (YD 116:1) quotes the PRI CHADASH who discusses another situation. What is the Halachah in a case in which there are no non-kosher animals in the area at all? Does the Jew still need to watch the milking? He explains that there are two types of decrees that the Rabanan enacted. One type is that the decree should always apply, regardless of whether the initial reason is still relevant. An example of such a decree is the prohibition from doing work on the afternoon of Erev Pesach. Although the reason for this decree -- in order to ensure that people are involved with preparing the Korban Pesach -- applies only in the times of the Beis ha'Mikdash, the Rabanan never stipulated as part of the decree that one may do work when there is no Beis ha'Mikdash. The second type of decree is one in which the Rabanan said that the decree applies only on condition that the reason for the decree remains relevant. If this is the nature of the decree against drinking the milk of Nochrim, then it could be that the Rabanan also prohibited the milk of Nochrim in a situation when there exists a plausible possibility that non-kosher milk was mixed into the kosher milk; when there is no reason to have any doubt, the decree does not apply and the milk is permitted.
The Pri Chadash understands that the decree against drinking the milk of Nochrim was made conditionally. Therefore, if there are no non-kosher animals in the vicinity, then the milk is permitted and the Jew does not have to watch the milking process at all. The Pri Chadash quotes this opinion in the name of the RADVAZ (see also CHASAM SOFER YD 107), and states that he himself relied on this when he was in the city of Amsterdam.
The Chasam Sofer (loc. cit.) argues strongly with the Pri Chadash and Radvaz. He cites many proofs that the decree prohibiting milk that was processed without Jewish supervision was enacted unconditionally, like the decree against doing work on the afternoon of Erev Pesach. Furthermore, he states that even if this was not the nature of the decree, the custom has already been established to be stringent. He concludes that one cannot rely on the opinion of the Radvaz to drink unsupervised milk of Nochrim.
HALACHAH: The situation today, in many places, is that Nochri-owned companies produce milk only from kosher animals, and there are government regulations to ensure that they do not mix any other liquid into the milk. The CHAZON ISH (YD 41:4) prefers the approach of the Pri Chadash. He states that the situation today is comparable to the case in which a Jew is sitting near the Nochri's herd during the milking. However, both the Pri Chadash and the Chazon Ish imply that this leniency applies only when it is very expensive to purchase milk that is produced or supervised by a Jew. In addition, it has always been the accepted practice in Eretz Yisrael to be stringent and to consume only milk produced or supervised by Jews (see TZITZ ELIEZER 16:25 in the name of the CHIDA). Therefore, in Eretz Yisrael, one must follow the prevalent custom and drink only milk produced or supervised by Jews ("Chalav Yisrael"). Moreover, it is not clear from the Chazon Ish that he actually ruled in accordance with the Pri Chadash, and, indeed, there are many who say that the Chazon Ish did not rule in accordance with the Pri Chadash (see CHELKAS YAKOV 2:38, who writes that the Chazon Ish personally told him that the milk of Nochrim is prohibited, even when the government regulates the production).
RAV MOSHE FEINSTEIN zt'l (IGROS MOSHE YD 1:47-9) gives another reason why one may rely on the companies that produce milk without the supervision of a Jew. He explains that the Torah considers information based on overwhelming evidence to be like fact. For example, the Gemara in Makos (7a) states that witnesses may testify that they saw a man and a woman commit immoral relations even when they did not see the actual act, but only a semblance of the act. This is because it is so clear that the act occurred that it is considered as fact. Accordingly, since it is known that an industrial dairy that adds unacceptable liquids into its milk will be fined heavily by the government and possibly lose its business license, it can be assumed beyond a doubt that the milk is kosher. This degree of certainty is akin to having witnesses watch the milking ("Anan Sehadi"). However, Rav Moshe himself states that it is appropriate for people who are meticulous in their fulfillment of the Mitzvos to be stringent and drink only "Chalav Yisrael." It is important to note that there are a number of Poskim who disagree with the ruling of the Igros Moshe and maintain that it is prohibited to drink milk of Nochrim that was not supervised by a Jew (see Chelkas Yakov loc. cit., BE'ER MOSHE 4:52, MISHNEH HALACHOS 4:103, and KINYAN TORAH 1:38). (Y. MONTROSE)