In the comment section of my post about the 2008 Bartenura Nebbiolo, Elyse asked:
What makes a wine kosher?
There are two methods for making kosher wine—the regular process of winemaking, but done only by Orthodox, Sabbath-observant Jews, and a process known as mevushal (“boiling” or “cooking”). Both methods are done under the supervision of a rabbi (known as a mashgiach) and include the use of only kosher products (i.e. the use of clay instead of egg whites or gelatin as fining agents to clarify the wine, barrels that are either new or have only been used for kosher wines, etc.)
The first method dictates how the wine is handled—only an observant Jew can handle all of the materials involved in the normal winemaking process. This means that while a non-Jew can give instructions on what to do, everything from vine to wine glass—harvesting the grapes, preparing them for fermentation, sampling the juice, bottling the wine, selling the final product, and pouring the wine into the glass—must be completed by someone who is Jewish.
The other method dictates how the wine is prepared—the wine, which is made through the normal winemaking process, must be cooked/boiled at a high temperature (about 176-185 F) or undergo flash pasteurization before bottling. This method creates mevushal wine. Both Jews and non-Jews can handle mevushal wine once it’s bottled, which makes it easier to sell and to serve.
In Israel, there is the additional requirement of following biblical agricultural law in order to be designated kosher. Therefore, kosher vineyards can only grow grapevines (no orchards, for example), and the vines need to be four years old before their grapes can be used to make kosher wine. Additionally, if the vineyard is located within biblical territory, the land must lay fallow every seven years. Finally, 1 percent of production is poured out in remembrance of the 10 percent tithe set aside for the Levites and priests of the First Temple.
Finally, not all wine is kosher for Passover. In order to have this designation, the wine not only has to be kosher, but also can’t have come into contact with grain, dough, or bread products.
I hope this helps, and thanks for asking. I’m sure it’s a question that many readers had!
**I used Jancis Robinson’s The Oxford Companion to Wine, 3rd Edition as background for writing this post.