Kashrut: History and Development
The consumption of food and drink, considered one of the great joys of life in the Bible, is subject to a number of restrictions in the Torah's legal passages. Among the land animals only certain types of mammals—cud-chewing species with split hooves—and a very small class of insects are approved, or kosher, for consumption by the Israelites, to whom biblical law is addressed. Only certain types of fowl are similarly acceptable, and only their eggs among those of the birds are to be eaten. Among sea creatures, only fish with fins and scales may be consumed.
The flesh of acceptable mammals and fowl could be consumed, but not their blood. One additional restriction on consuming such meat is the ban on cooking a kid in its own mother's milk.
Rabbinic Judaism elaborated a series of practices intended to provide the details of behavior for putting the biblical restrictions into practice. The rabbis of Judaism's formative period laid out complex rules for the slaughtering of animals and for the removal of blood from meat by salting it and soaking it in water. Most notably, from the ban on cooking a kid in its mother's milk, repeated three times in the Torah, the rabbis made a tripartite ban on combinations of the taste from the meat of a kosher animal (even kosher fowl) with the taste of the milk of a kosher mammal. One is forbidden by rabbinic law to cook such a combination, to consume it, or to derive economic benefit from it in any way.
Over centuries of development, with popular practice influenced by the rulings of rabbinic authorities, these last restrictions developed into a system of separation articulated in great detail: separate sets of utensils for milk and meat, for example, and, in many homes, separate color-coded tablecloths, placemats, and dishtowels. Elaborate systems were developed for undoing (or letting pass) near-infractions of these rules—such as the accidental inclusion of a very small amount of milk in a meat dish, or vice-versa—or outright violations.