Food that is not in accord with Jewish law is called treif (טרײף or treyf, derived from טְרֵפָה trēfáh). In the technical sense, treif means "torn" and refers to meat which comes from an animal containing a defect that renders it unfit for slaughter. An animal that died through means other than ritual slaughter (or by a botched slaughter) is called a neveila which literally means "an unclean thing".
Many of the basic laws of kashrut are derived from the Torah's Books of Leviticus and Deuteronomy, with their details set down in the oral law (the Mishnah and the Talmud) and codified by the Shulchan Aruch and later rabbinical authorities. The Torah does not explicitly state the reason for most kashrut laws, and many varied reasons have been offered for these laws, ranging from philosophical and ritualistic, to practical and hygienic.
The laws of kashrut derive from various passages in the Torah, and are numerous and complex, but the key principles are as follows:
The following rules of kashrut are not universally observed:
This last view has been rejected by most classical and modern Jewish authorities . For example Maimonides holds that a Jew is permitted to seek out reasons for the laws of the Torah.
The Torah prohibits 'seething the kid (goat, sheep, calf) in its mother's milk', a practice cruel only in concept, which would not be understood as cruelty by either the kid or its mother and would not cause them additional suffering; but which might still potentially inflame a human's taste for ultimate power over those creatures who are weaker. Thus, kashrut prohibits the practice itself, even if the resulting mixture is to be discarded.
However, these risks can usually be reduced to insignificance simply by ensuring the meat is properly cooked; similarly the diseases and toxins which occur in the food of animals are also dangerous when those foods are eaten directly (eg. eating the vegetables, seeds, and fruit that pigs eat, rather than the pigs themselves), something which the food laws don't particularly forbid. The claims that the laws have a hygiene/health purpose has therefore fallen out of favour among Biblical scholars, particularly since there are obvious dangers that the laws do not cover; for example, there are no prohibitions on the types of fruit and vegetables which can be eaten, even though there are many poisonous herbs, seeds, berries, and fruits.
Nevertheless, some continue to pursue the idea that the food laws introduce health benefits. In 1953, Dr. David I. Macht, an Orthodox Jew who is one of the primary proponents of the scientifically discredited theory of biblical scientific foresight, conducted toxicity experiments on many different kinds of animals and fish. His experiment involved lupin seedlings being supplied with extracts from the meat of various animals; Macht reported that in 100% of cases, extracts from ritually unclean meat inhibited the seedling's growth more than that from ritually clean meats. In addition, Dr. Macht's research indicated that mixtures of meat and milk, and meat that wasn't ritually slaughtered, appeared to be more toxic to lupin seeds than meat from other sources. Macht's claim that his methodology, known as phytopharmacology, could have any conclusions in relation to human consumption, has never been scientifically corroborated by independent researchers, and is regarded by the scientific community as not being mainstream science; at the request of a Seventh-day Adventist Church publication, Macht's study was explicitly challenged by a series of senior biologists
Hasidism believes that everyday life is imbued with channels connecting with Divinity, the activation of which it sees as helping the Divine Presence to be drawn into the physical world; Hasidism argues that the food laws are related to the way in which such channels, termed sparks of holiness, interact with various animals.
According to the teachings of Hasidism, sparks of Holiness are released whenever a Jew manipulates any object for a holy reason (which includes eating, if it is done with the intention to provide strength to follow the laws of the Torah); however, in the view of Hasidism, not all animal products are capable of releasing their sparks of holiness. The Hasidic argument is that God designed the animals in a way that gives clear signs about whether sparks can be released from them or not, the signs being expressed in the biblical categorization into ritually clean and ritually unclean; the signs themselves are not believed to be the cause of the animal being kosher, and hence if a cow happens to born with a fully fused hoof, it does not become non-kosher on this basis alone.
There is also the view that obedience to the laws of kashrut is a necessary precondition for a Jew to be able to reach his utmost spiritual capacity. According to this understanding, the intention of the laws is to instil obedience in the base, animalistic sectors of a person's life in order to achieve obedience and spirituality in the more lofty pursuits of Judaism.
According to Christian theologian Gordon J. Wenham, the purpose of kashrut was to help Jews maintain a distinct and separate existence from other peoples; he alleges that the effect of the laws of kashrut was to prevent socialization and intermarriage with non-Jews, preventing Jewish identity from being diluted. Wenham argued that since the impact of the food laws was a public affair, this would have enhanced Jewish attachment to them as a reminder of the special status of Jews.
Deceased anthropologist Marvin Harris proposed that the Jewish prohibition against pork results from mundane socio-economic concerns. Although wild pigs forage in the forests, there are no such environments for them in the region that was Canaan, and consequently they must instead be fed grain; however, the grain which pigs eat is also that eaten by people, and so the pigs would compete with humans for survival during years of bad harvest. As such, raising pigs could have been seen as wasteful and decadent; Harris cites examples of similar ecological reasons for religious practices, including prohibitions against pork, in other religions of the world.
In 1966, British cultural anthropologist Mary Douglas published the influential study Purity and Danger; this study made the proposal that prohibited foods were those which did not seem to fall neatly into any category, as an extention of the observation that people in states of liminality (in which persons are at the fringes of a group) are often fraught with danger. For example, she argued that pigs were declared unclean in Leviticus because the place of pigs in the natural order is superficially ambiguous, since they shared the cloven hoof of the ungulates, but do not chew cud.
According to other theories, the practice of kashrut serves as a daily exercise in self-discipline and self-control, strengthening the practitioner's ability to choose other difficult paths. The ability to rationally curb one's most basic appetites can be seen as the prerequisite to living in a civilized society. Also, Jews consider the aspects of kosher slaughter which emphasize and incorporate the need to avoid unnecessary suffering of the animal a reminder to the believer that having the power of life and death or to cause suffering, even to a farm animal born and bred to be eaten, is a serious responsibility rather than a pleasure to be sought after; and that to actually indulge in pleasure in the power to cause suffering, even in so common a practice as hunting, is to damage our own moral sensibilities.
The prohibition against eating the fruits of a tree for the first three years also represents a capacity for self-discipline and self-denial, as well as a lengthy period of appreciation for the bounty of God, prior to losing oneself in its enjoyment. Similarly, the requirement to tithe one's harvest, aside from the social justice aspect, serves as a reminder that this material wealth is not purely the result of one's own efforts, but represents a gift from God; and as such, to share the gift with one's fellows does not represent a real loss to anyone, even oneself.
Conservative Judaism follows a number of leniencies, including:
Although Reconstructionist Judaism and some perspectives within Reform Judaism encourage individuals to follow some or all aspects of the kashrut rules required by the more traditional branches, these branches do not require their observance and do not maintain their own sets of required rules.
Many Jews who do not meet the complete requirements of kashrut nevertheless maintain some subset of the laws; for instance, abstaining from pork or shellfish. Many Jews will likewise avoid drinking milk with a meat dish. Similarly, many keep a degree of kashrut at home while having no problems eating in a non-kosher restaurant, or will follow leniencies when eating out that they would not follow at home.
In the summer of 2004, a controversy arose in New York City over the presence of copepods (tiny crustaceans) in the city water supply. While some authorities hold that these creatures are microscopic and therefore negligible, others note that they are almost the size of a small insect, such as a gnat, and far larger than bacteria or other single-celled creatures; in fact can be detected by the naked eye. As of this writing a definitive ruling has not been produced as to whether copepods affect the kosher status of water, but many families have begun using filters on their drinking and cooking water supply.
By extension, the broader sense of the word kosher has the meanings legitimate, acceptable, permissible, genuine, or authentic. For example, the Babylonian Talmud uses kosher in the sense of virtuous, when referring to the Dãrayavahush I (known in English, via Latin, as Darius) as a "kosher king"; Darius, a Persian King, assisted in building the Second Temple. It is this wider sense of kosher which has entered the colloquial language of certain groups of non-Jewish English speakers, particularly in the East End of London (including Cockney communities), which had a large Jewish community before the 20th Century; this use of kosher is consequently heard frequently in the vocabulary of stereotypical East End criminals and market-stall holders, in both literature and film.
The word kosher is also part of some common product names. Sometimes it is used as an abbreviation of koshering, meaning the process for making something kosher; for example, kosher salt is a form of salt which has irregularly-shaped crystals, making it particularly suitable for preparing meat according to the rules of kashrut, because the increased surface area of the crystals absorbs blood more effectively. At other times it is used as a synonym for jewish tradition; for example, a kosher dill pickle is simply a pickle made in the traditional manner of Jewish New York City pickle makers, using a generous addition of garlic to the brine, and is usually not particularly compliant with the traditional Jewish food laws. For these reasons, kosher-style has become frequently used in the food industry of countries with a heavy Jewish influence, from delis to restaurants, and even to street vendors.
Many vegetarian restaurants and producers of vegetarian foods do in fact acquire a hechsher, certifying that a Rabbinical organization has approved their products as being kosher. In addition to the above concerns, the hechsher will usually certify that certain suspect vegetables have been checked for insect infestation, and that steps have been taken to ensure that any cooked food meets the requirements of bishul Yisrael.
Most vegetables, particularly leafy vegetables (lettuce, cabbage, parsley, dill, etc.), must be thoroughly checked for insect infestation (see link below for video instruction on proper checking procedure from the OU). The consumption of insects involves between three and six violations of Torah law; so, according to Jewish Law, it is a greater sin than the consumption of pork. The proper procedure for inspecting and cleaning will vary by species, growing conditions, and the views of any particular rabbi.
The situation is not always reversible, however; although pareve food can contain neither meat nor dairy, that label on a product cannot be always used by vegetarians as a reliable indication, since kashrut considers fish to be pareve. Because of potential issues of mixing meat and fish (see Fish and seafood) some kashrut supervising authorities specifically indicate the presence of fish products when they are found in pareve foods.
People who have specific dietary needs should be aware that their standards for certain concepts may differ from the halachic standards for similar concepts.
Kashrut prohibits slaughter of an unconscious animal, and the slaughtering is done by cutting the front of the throat first. Some animal rights groups object to kosher slaughter, claiming that it can take several minutes for the animal to die and can often cause suffering. Since the spinal cord is not severed completely at the first cut, it is thought that the slaughtered animal's nervous system continues to function during the initial moments of the slaughter, causing the animal to undergo an agonisingly slow and painful death. In 2003 in the UK, an independent advisory group - the Farm Animal Welfare Council (FAWC) - concluded that the way Kosher (and Halal) meat is produced causes severe suffering to animals and should be banned immediately. Kosher and halal butchers deny their method of killing animals is cruel and expressed anger over the recommendation .
Specific kashrut laws counter some of the rituals of ancient times, such as eating only one leg of a live animal so that people would not have to deal with eating the entire animal at one time (Babylonian Talmud Sanhedrin 56b); this law applies even to non-Jews and is part of the Noahide Laws. Some authorities have ruled that any unnecessary suffering by the animal can render otherwise kosher meat treife.
The Rabbinical Assembly, the USA's association of rabbis in Conservative Judaism, has endorsed a proposed certification, called Heksher Tzedek, which would signify that food was produced under safe and just working conditions; the specific requirements for implementing the certification remain under development, but the current plan is for it to be an additional certification, rather than a replacement for kosher certification. In Israel, a new movement has gone further, demanding that food-selling establishments (grocers and restaurants) should only be considered fully kosher if their employees are paid a decent wage and treated fairly, and if the buildings have access for the handicapped; the movement envisage this as requiring an additional second certificate of kashrut, rather than as replacing the standard certification.
A number of arguments have been raised against these proposals. Several critics of the suggestions believe that entities providing Kashrut certification shouldn't be involved in the politics of labour. The labour laws of different countries can vary widely in the extent to which they directly benefit the employee's welfare, rather than the employer's income, but certain critics believe that their country's laws about labour still would not need supplementation by rabbinic certifications; for example, a number of Rabbis have argued that the laws of the USA already include labour regulations matching those of the Torah, and provide several mechanisms for individuals to report and prosecute breaches of these laws. However this information is never made transparent to consumers through certification or product markings. Another concern which has been raised is the possibility that rabbinical authorities may become legally culpable for accidents that occur in environments which they have previously certified as safe; related to this is the concern that there is currently no concretely proposed mechanism for monitoring the employer's continued compliance with the certification, particularly with things like the Heksher Tzedek where there is a need to monitor a vaguely defined quality - the fairness of the employer.
Although reading the label of food products can identify obviously non-kosher ingredients, some countries allow manufacturers to neglect to mention certain ingredients; such 'hidden' ingredients can include lubricants, flavourings, and other additives, which in some cases, such as when natural flavourings are used, are more likely to be derived from non-kosher substances. However, producers of foods and food additives can contact Jewish religious authorities to have their products certified as kosher: this would most likely involve a visit to the manufacturing facilities by a committee from a rabbinic organisation, rather than by an individual rabbi, in order to inspect the production methods and contents, and if everything is sufficiently kosher a certificate would be issued.
Manufacturers sometimes identify the products which have received such certification by adding particular graphical symbols to the label; these symbols are known in Judaism as hechsherim. The hechsheirim of certain Jewish authorities are sometimes considered invalid by certain other Jewish authorities; the certification marks of the various rabbis and organisations are too numerous to list, but one of the most commonly used is that of the Union of Orthodox Congregations, who use a U inside a circle, symbolising the initials of Orthodox Union. A single K is sometimes used as a symbol for kosher, but since many countries do not allow letters to be trademarked (the method by which other symbols are protected from misuse), it only indicates that the company producing the product claims that it is kosher.
Many of the certification symbols are accompanied by additional letters or words to indicate the category of the product, according to Jewish religious law; the categorisation may conflict with legal classifications, especially in the case of food which Jewish religious law regards as dairy, but legal classification does not.
In many cases constant supervision is required, because, for various reasons, such as changes in manufacturing processes, products which were once kosher may cease to be so; for example, a kosher lubricating oil may be replaced by one containing tallow, which many rabbinic authorities view as non-kosher. Such changes are often co-ordinated with the supervising rabbi, or supervising organisation, to ensure that new packaging, which will not suggest any hechsher or kashrut, is used for the new formulation. But in some cases, existing stocks of pre-printed labels with the hechsher may continue to be used on the now non-kosher product; for such reasons, there is an active grapevine among the Jewish community discussing which products are now questionable, as well as products which have become kosher but whose labels have yet to carry the hechsher. There are also newspapers and periodicals covering the subject of kashrut products.
Advertising standards laws in many jurisdictions prohibit the use of the phrase kosher in a product's labelling, unless it can be shown that the product conforms to Jewish dietary laws; however, the legal qualifications for conforming to Jewish dietary laws are often defined differently in different jurisdictions. For example, in some places the law may require that a rabbi certify the kashrut nature, in others the rules of kosher are fully defined in law, and in others still it is sufficient that the manufacturer only believes that the product complies with Jewish dietary regulations. In several cases, laws restricting the use of the term kosher have later been determined to be illegal religious interference.