Kosher wine is made just like other table wine, with an extra set of rules to make it consistent with Jewish dietary law. In order for a wine to be deemed kosher (Yiddish for "proper" or "fit"), it must be made under the supervision of a rabbi. The wine must contain only kosher ingredients (including yeast and fining agents), and it must be processed using equipment rabbinically certified to make kosher wines. No preservatives or artificial colors may be added. The wine can only be handled -- from the vine to the wineglass -- by Sabbath-observant Jews, unless the wine is mevushal.
Mevushal wines, unlike ordinary kosher wines, can be handled and served by non-Jews. To be considered mevushal, a wine must be heated to 185 degrees F. Extended exposure to high temperatures can threaten a wine's character, but producers have developed flash-pasteurization techniques that minimize the effect on the wine's flavor.
"Flash pasteurization was in its infancy just five or six years ago; we've since tweaked it so it's now more precise and on target," said Jay Buchsbaum, vice president of marketing for Royal Wine Corp. "At the same time as it satisfies the rabbinical requirements, we don't want to harm the wine."
Wines kosher for Passover must also be free of certain additives, such as corn syrup and legumes. Most kosher wines are already approved for Passover, but producers of Concord-based wines (such as Manischewitz) that are sweetened with corn syrup must produce special "kosher for Passover" bottlings, which are labeled as such.