- The ultimate source for the laws of kosher eating, or kashrut, is the Torah: the five books of the Jewish bible. The relevant laws are first stated in chapter 11 of Leviticus and are reiterated and expounded in Deuteronomy 14. Through the millennia, the laws have been interpreted and applied to new situations, resulting in what we now know as the requirements for kosher food. The word "kosher" actually means "fit" and applies not only to food. In the context of food, kosher laws cover both what can be eaten and how it must be prepared.
- Only meat from animals that both chew their cud (that is, they are ruminants) and have a split hoof can be consumed. So meat from cows and sheep is kosher, but meat from horses, rabbits and dogs is not. In addition, the animal must be killed in a specific way referred to as "schechitah," which is intended to minimize suffering. The carcass must pass inspection for diseases and other defects, and the blood must be completely removed.
- Species of fish that have both fins and scales are kosher, while other sea creatures are not kosher. Salmon, whitefish and tuna are kosher, but shellfish, sea mammals and scavengers such as catfish are not. The Torah allows 21 types of birds, including chickens and ducks but excluding all predators and scavengers. Shechitah, the specific method of killing the animal, applies to fowl as well.
- All types of fruit, vegetables and gain are kosher. However, it is important that they be free of insects, which are not kosher. Wine and grape juice are in a special category. Due to their ritual use, they must be certified kosher, since the Torah requires they be produced by observant Jews. Also, produce grown in Israel is subject to laws of tithing and the sabbatical year.
- All foods are classified as either meat, dairy or "pareve." Pareve food includes fish and eggs, so it does not compare directly to a vegetarian or vegan diet. The prohibition against mixing meat and dairy has its source in a verse of Exodus, which makes it unacceptable to cook a baby animal in its mother's milk. The general interpretation has led both to prohibition against including both meat and dairy items in a single meal and to observance of waiting periods between eating both types of food. Even separate dishes are used for strict observance of kashrut.
- In addition to the requirements about what food can be eaten, great care is taken to ensure that kosher food does not come into contact with nonkosher food directly or indirectly. Different sets of dishes and utensils are used for dairy and meat items, and manufacturers are supervised to ensure that equipment is used only for kosher food or is properly cleaned in between. Purchased prepared food must have a special symbol called a "hechsher" that certifies that it was treated and prepared according to kosher laws.
- The general rule is that products from kosher animals are kosher themselves, if they meet the preparation requirements. For example, milk from kosher animals is permitted, and eggs from kosher fowl are kosher. Eggs must be checked to ensure no blood is present, however. The one exception is that bees are insects and thus not kosher (only four species of locust are kosher of all the insects), but honey is permitted. And finally, additional laws apply to food during the Passover holiday, restricting use of certain grains and other plant-based foods that are kosher during the rest of the year.
