Blessing by a rabbi makes a wine kosher.
It is a common misconception that wine need only be blessed by a rabbi to make it kosher (Yiddish, from Hebrew kāshēr, meaning “proper” or “fit”). To be kosher, a wine must also contain only kosher ingredients. For example, fining agents may not be derived from animal by-products, which rules out egg whites, casein (a dairy derivative), and isinglass (air bladders of fish). The wine can only be handled—from the vine to the wineglass—by Sabbath-observant Jews unless the wine is mevushal (Yiddish for “cooked”), which involves heating the wine until it is pasteurized. During Passover, Jews drink four cups of wine (for the four promises the Lord makes to His people in Exodus 6:6-7) at the Seder meal, which occurs on the first two nights of the holiday—March 27-April 4 in 2021. To be kosher for Passover, wines must also be free of certain additives, such as corn syrup, which producers of concord grape wines (such as Manischewitz) sometimes add.