Wine is central to many Jewish holidays and festivities. That wine must be kosher. In response to the large Jewish population of the United States, along came Manischewitz, a company that caters to the Jewish community with it's well-known Manischewitz Kosher Wine, among other kosher food items. Their wine is sweet, thereby giving the impression, over time, that to be kosher meant to be sweet. As the Jewish population has since learned, kosher wine can be dry and still be tasty and kosher.
To be a kosher wine, it must be made, from start to finish, under rabbinical supervision and must be handled by a Sabbath-observant Jew. While none of the ingredients used to make wine are considered non-kosher, some of the fining agents used are not strictly kosher. Also, to be kosher, in it's strictest sense, a wine handled or served by non-Jew or a non-observant Jew cannot be used for sacramental purposes.
To be sure a kosher wine has been made by the set standards and is appropriate for sacramental uses, it will be labeled one of two ways - mevushel or non-mevushel. A Mevushel wine is one that has been, quite literally, cooked. In earlier days, the wine would be boiled, but this was not conducive to retaining the wines aroma and flavor, nor to the aging process. These days, a flash pasteurization process is used, that is much gentler on the finished product. By producing a mevushel wine, it can now be handled and served by anyone, and still be consumed by those who follow even the strictest codes of kosher dietary regimens.
A non-mevushel wine, on the other hand, is made in more traditional wine-making methods, under the supervision of a Sabbath-observing Jew to still be considered kosher, resulting in a better tasting wine. However, if a non-observant Jew or a non-Jew comes into contact with this wine, even accidentally, it can no longer be considered for sacramental purposes, or consumed by those who follow strict kosher dietary law.
There are some fine kosher wines produced world-wide. To find them, visit www.kosherwine.com.