Traditional Jewish practice forbids the consumption of some types of food (certain varieties of animals, animals slaughtered by any but the accepted method, the blood of mammals or birds) and some combinations of foods (roughly, meat with milk products). It mandates kitchen practices that help maintain those restrictions. These laws, known collectively as kashrut (literally, "fitness"), are observed in varying degrees among Jewish families and individuals. For those who choose to observe some or all of the system of kashrut, it serves as a frequent reminder of their distinct identity as Jews.
Theology and Themes: Many explanations have been offered for each aspect of kashrut. The Torah suggests that the Israelites attain unique holiness through food restrictions that distinguish them from other peoples. Some later explanations are framed in behavioral categories internal to Judaism, such as inculcating kindness and preventing cruelty to animals. Others are the insights of historians and anthropologists, frequently on the basis of comparison with other religious systems. None has proved universally satisfactory, but many have served to bolster the desire of some Jews to observe these challenging restrictions.
History and Development: The Torah is the source of limitations on what foods from animal sources may be consumed and of the ban on "cooking a kid in its mother's milk." Rabbinic tradition interprets those prohibitions, filling in operative details and setting up further restrictions to provide greater assurance that the Torah's bans are not violated. Over centuries of application and interpretation, these restrictions have been extended and refined. Modern Jewish thinkers and movements vary in the degree to which they advocate the observance of kashrut. Some have tried to blend it with such contemporary concerns as vegetarianism and environmentalism.
Kosher Food: Food from animal sources is subject to many conditions. Only certain species of mammals and birds are kosher, and then only if slaughtered in a particular fashion and found healthy upon inspection. The prohibition on consuming blood requires that meat be salted and soaked. Fish with fins and scales are kosher, and their flesh requires no such special treatment.
Today, Jews who observe kashrut rely on recognized supervision agencies whose symbols on packaged foods or whose certificates in shops and restaurants testify to the acceptability of the food within.
Keeping Kosher: Preventing the mixing of meat products and milk products has led to the practice of maintaining separate sets of cookware, tableware, and flatware for meat and dairy. Some households also have items used for neither meat nor milk (this category is called pareve, or neutral); food prepared using these can be eaten with either meat or dairy.
Establishing a kosher kitchen requires some work, but the regularities are not difficult to maintain. Making an existing kitchen kosher may involve replacing some equipment, but many items can be made kosher and some need no treatment at all. With good will, flexibility, and creativity, individuals can "keep kosher" in non-kosher homes and restaurants.
Ask an average person to describe kosher food and they might say it is food "blessed by a rabbi." The word "kosher," however, is Hebrew for "fit" or "appropriate" and describes the food that is suitable for a Jew to eat. With its roots in the Hebrew Bible, the system of defining which foods are kosher was developed by the rabbis of late antiquity. Its application to changing realities has been the work of subsequent generations, including our own.
Close readers of the Torah might notice that according to the book of Genesis, vegetarianism was commanded by God as the ideal diet (see Genesis 1:29). However, in the course of the biblical narratives, this changed to include a variety of different animals. According to the Torah (Leviticus, chapter 11), only certain kinds of animals are considered inherently kosher. For land animals, any creature that both chews its cud and has split hooves is kosher. For sea creatures, any fish that has both fins and scales is acceptable, and for birds, only those birds approved by the Torah (or others that later authorities have judged to be like them, a list that excludes scavengers and birds of prey). In addition, it is repeated three times in the Torah that it is forbidden to cook a baby goat in its own mother's milk.
The rabbis in the Talmud further developed these principles of kashrut. In order to consume kosher land animals and birds, it is necessary to slaughter them in a prescribed way, in a manner that has been described as a more humane method than is practiced commercially. In addition, the prohibition of cooking a baby goat in its own mother's milk is the basis for the complete, physical, hermetic separation of all milk and meat products. These are the fundamental elements of kashrut.
All questions, problems or issues about keeping kosher ultimately revolve around the basic principles of kashrut described above. Usually, the questions have to do with the last basic element, the complete separation of milk and meat products. The use of different sets of dishes and pots and pans, developed in order to ensure a greater separation between milk and meat foods. This is also the basis of waiting several hours after eating a meat dish before eating a dairy product, so that the two types of food shouldn't even mix together in our stomachs! (A much shorter wait is required after some dairy foods before consuming meat.)
Whether a particular food is considered kosher or not usually has to do with whether any substance or product used in its manufacture was derived from a non-kosher animal or even an animal that is kosher but was not slaughtered in the prescribed manner. Rabbinic supervision of the production of food (a practiced called hashgachah) enables it to carry a "seal of approval" (but no, it is not "blessed by a rabbi").
There are three categories of kosher foods:
1) dairy foods, such as cheese, milk, yogurt, ice cream, etc.
2) meat foods, which includes all kosher animals and fowl slaughtered in the prescribed manner, and their derivative products.
3) pareve foods, using a Yiddish word meaning "neutral." These are foods that are neither dairy nor meat, such as eggs and fish, tofu, nuts, seeds, fruits and vegetables, and the like, provided they are not prepared with any milk or meat products.
In keeping kosher, it is necessary to keep all dairy and meat foods completely separate. Pareve foods, however, may be mixed in and served with either category of food since these foods are neither milk nor meat.
For definitions of terms used and more in-depth resources on Kashrut, please visit myjewishlearning.com