Wine can present a unique problem. There is an ancient prohibition, alluded to in the book of Daniel, against drinking the wine of gentiles. This prohibition includes any wine that was not stored in a closed and sealed vessel and which was touched by a gentile. The reason for this prohibition is the concern that drinking the wine of gentiles might cause Jews to be tempted to assimilate into gentile culture and to intermarry.

Further reading: On the dangers of overindulgence in wine in general, see A Concise Guide to the Sages, pp. 15, 141.

One may not drink wine made by gentiles. The same restriction applies to any beverage made by gentiles that is produced by refining or processing wine (cognac, brandy, champagne, and the like). It does not apply to other liquors that are not produced from grapes. Therefore, beer, apple cider, whiskey, vodka, and the like, can all be kosher even when produced by gentiles. Sometimes a problem can arise with regard to their consumption during Passover; see the section dealing with the halakhot of Passover.

If the wine underwent a process of cooking before a gentile touched it, no prohibition applies to it; this is the halakha with regard to pasteurized wine. If someone is hosting non-Jewish guests, he is advised to use cooked wine, or not to bring wine to the table at all, in order to avoid problems of kashrut and a possible uncomfortable situation.

There are alcoholic drinks that, while generally kosher, sometimes involve kashrut problems, such as a mixture of milk with vodka or liquor, a mixture of wine with whiskey, or moth larva that is found in certain types of tequila (mescal). It is recommended to consult a rabbi who specializes in kashrut or to purchase only products that have a reliable kosher certification.