Laws of the prohibition of wine, milk, bread and other products made by a non-Jew.
1. Our sages wished to prevent an exceeding closeness between Jews and Gentiles because usually, such closeness leads directly to assimilation. We know that the most of communication and friendliness arise at the table therefore they forbade a range of products made by a non-Jew, even though they can be considered fully kosher. They were especially strict regarding the wine because the first case of assimilation happened due to wine that Midianite women gave to Jews to drink and afterwards offered themselves as a prize if the Jew would bow to their idol.
2. Any grape wine (or grape juice) touched by a non-Jew is forbidden to us. For this reason, where there’s a production of kosher wine or grape juice, only religious Jews are present, and while the bottles have not been corked, no one else is allowed to touch them. In the olden times they hadn’t boiled their wine, and this is why our sages didn’t prohibit it. Many types of grape juice have been boiled as a result of pasteurization. Usually bottles of kosher wine or grape juice contain inscription “mevushal” (boiled) or “eino mevushal” (not boiled).
3. Any alcohol beverages are prohibited in the presence of non-Jews. Nevertheless, if a drink doesn’t contain grapes, one may buy it from a non-Jew and drink it at home, as for example some Jews buy vodka from non-Jews.
4. As it has been mentioned, one of the reasons for prohibition of food made by a non-Jew is the danger of assimilation. But there is another reason, which is fear that a non-Jew will try to feed us something non-kosher, and this is why we are forbidden to buy milk and dairies made by a non-Jew. The majority of Gentile farmers own pigs and horses (and in Arabic countries they also have camels and donkeys) at a farm, and it is no wonder, that they might mix cow milk with the milk of another animal that is be non-kosher. There is a visible advantage in such a non-kosher mixture because mixed milk will stay good longer than pure cow milk (if one leaves a mixture of kosher and non-kosher milk in direct sun light or a warm place, it will turn sour much later than pure kosher milk). Even nowadays when in many countries it is officially prohibited to mix cow milk with other sorts of milk however the checks the government performs is not sufficient, according to majority of Rabbis. This is especially true since the penalty for mixing cow and pig milk together is usually very small. Most righteous Jews drink only the milk, containing inscription “Cholov Isroel” (milk manufactured by Jews). Nevertheless there is an opinion of a Rabbi who allowed to drink ordinary milk when there is no other milk available, and some people follow this opinion even today, while we can note, that the Rabbi himself drank only Jewish milk. As for cheeses problems of kashrus could arise in the process of cheese production, and that’s why they need real “Hashgacha” (Rabbis’ supervision) in all cases.
5. Our sages forbade us bread baked by a non-Jew. This prohibition however was made more lenient because one can’t do without bread altogether, therefore they allowed bread, if during the process of baking a Jew had at least tossed a couple of logs in the oven. In places where there is no other bread available one is allowed to eat ordinary bread. Certainly, one is allowed to eat such bread only in case he can be sure that it is kosher per se, that is none of animal fats had been added to it, and this is the reason why “Hashgaha” (Rabbis’ supervision) is required here as well.
6. The Rabbis forbade the food cooked by a non-Jew even though it has no non-kosher ingredients. This prohibition concerns only the types of food that cannot be consumed raw and are sufficiently important to be offered to guests. As for the prohibition of food, cooked by a non-Jew there is a serious difference between Sephardic and Ashkenasic laws. For the Ashkenasim it is sufficient that a Jew lights the fire in the oven, and even if a non-Jew lights up the fire from a Jewish fire this food is also allowed. For this reason in many restaurants the Jew lights up only a pilot light. For Sephardic Jews this is not sufficient, they require a Jew taking part in actual cooking of the food. For instance, a Jew could put a pan on the stove, and a non-Jew will be allowed to stir the food in it, or vice versa. According to this it’s possible that a Sephardic Jew will not be allowed to eat in some Ashkenasic kosher restaurants.