I think 犹太的 is a proper word reflect to kosher.
I don't know what is the restriction of kosher, but I believe it's something similar to halal. Halal is translated to 清真的, which emphasize the religion specific. Because Islam is translated to 清真教 at the time it was just introduced to China, although nowadays we use 伊斯兰教 to refer the religion, and 清真 to reflect to halal.
Compare halal and kosher, I believe 犹太的 make sense since it emphasize the religion specific. Regarding 洁食 mentioned by food_lover, I think it's not a proper translation to Chinese people. Because 洁食 means clean food in Chinese, it implies food which are not kosher is dirty. This may acceptable to Jewish, but definitely kind of offensive to people who don't believe in the religion. So I think a neutral word like 犹太食品 would be the best for kosher food.