isinglass finings are also used in the production of kosher wines, although for reasons of kashrut, they are not derived from the beluga sturgeon, because this fish is not kosher. whether the use of a nonkosher isinglass renders a beverage nonkosher is a matter of debate in jewish law. rabbi yehezkel landau, in "noda b'yehuda", first edition, yore deah 26, for example, permits such beverages. this is the position followed by many kashrut-observant jews today.