Kosher foods are those that conform to the regulations of kashrut (Jewish dietary law). Food that may be consumed according to halakha (Jewish law) is termed kosher (pronunciation: //) in English, from the Ashkenazi pronunciation of the Hebrew term kashér (כָּשֵׁר, pronunciation: //), meaning "fit" (in this context, fit for consumption). Food that is not in accordance with Jewish law is called treif (Yiddish: טרײף, pronunciation: //, derived from Hebrew: טְרֵפָה trāfáh) meaning "torn."
The Torah permits only animal species which both chew the cud and have cloven hooves. Four animals are specifically identified as being forbidden for this reason; the hare, hyrax, camel, and pig – although the camel has two toes, and the hare and hyrax are hindgut fermenters rather than ruminants.
The Torah lists winged creatures which may not be consumed, mainly birds of prey, fish-eating water-birds, and bats. The Torah permits any fish residing in "the waters" (seas and rivers) that has both fins and scales.
In addition to meat, other produce of forbidden species and from unhealthy animals, were banned by the Talmudic writers. This included eggs (including fish roe) and milk, as well as derived products such as cheese and jelly, but did not include materials merely "manufactured" or "gathered" by animals, such as honey (although, in the case of honey from animals other than bees, there was a difference of opinion among the ancient writers). According to the rabbinical writers, eggs from ritually pure animals would always be prolate ("pointy") at one end and oblate ("rounded") at the other, helping to reduce uncertainty about whether consumption was permitted or not.
The classical rabbinical writers imply that milk from an animal whose meat is kosher is also kosher. As animals are considered non-kosher if after being slaughtered they are discovered to have been diseased, this could make their milk retroactively non-kosher. However, by adhering to the principle that the majority case overrules the exception, Jewish tradition continues to regard such milk as kosher, since statistically it is true that most animals producing such milk are kosher; the same principle is not applied to the possibility of consuming meat from an animal which has not been checked for disease. Rabbi Hershel Schachter, a prominent rosh yeshiva at Yeshiva University, has made the bold claim that with modern dairy farm equipment, milk from the minority of nonkosher cows is invariably mixed with that of the majority of kosher cows, thus invalidating the permissibility of consuming milk from a large dairy operation; the Orthodox Union, however, released a statement declaring the milk permissible based on some leniencies.
Breast milk from a human female is permitted. However, authorities assert breast milk may be consumed directly from the breasts only by children younger than four (five if the child is ill), and children older than two were only permitted to continue to suckle if they had not stopped doing so for more than three consecutive days.
The situation of cheese is complicated as hard cheese usually involves rennet, an enzyme which splits milk into curds and whey. Most forms of rennet were formerly derived from the stomach linings of animals, but currently rennet is most often made recombinantly in microbes. Because the rennet could be derived from animals, it could potentially be nonkosher. Only rennet made recombinantly, or from the stomachs of kosher animals, if they have been slaughtered according to the laws of kashrut, is kosher. If a kosher animal is not slaughtered according to the halakha, the rennet is not kosher. Rennet is not considered a meat product and does not violate the prohibition of mixing meat and dairy.
Jacob ben Meir, one of the most prominent medieval rabbis, championed the viewpoint that all cheese was kosher, a standpoint which was practiced in communities in Narbonne and Italy. Contemporary Orthodox authorities do not follow this ruling, and hold that cheese requires formal kashrut certification to be kosher; some even argue this is necessary for cheese made with nonanimal rennet. In practice, Orthodox Jews, and some Conservative Jews who observe the kashrut laws, eat cheese only if they are certain the rennet itself was kosher. However, Isaac Klein's tshuva authorized the use of cheese made from non-kosher rennet, and this is widely practised by observant Conservative Jews and Conservative institutions.
The Yoreh De'ah argues that if there is blood in the egg yolk, then hatching must have begun, and therefore consumption of the egg would be forbidden. Modern Orthodox Jews adhere to these requirements; however, the Ashkenazi Orthodox Jews treat an egg as nonkosher if blood is found anywhere within it. Sephardi Orthodox Jews consider only blood in the yolk to be a problem, and treat eggs with blood in the albumen as legitimate food if the blood is removed before use.
Today, when battery eggs form the majority of available produce, many permit the egg with a blood spot following the removal of any actual blood; battery eggs are unlikely to be able to form a viable embryo.
Gelatin is hydrolysed collagen, the main protein in animal connective tissue, and therefore could potentially come from a nonkosher source, such as pig skin. Gelatin has historically been a prominent source of glue, finding uses from musical instruments to embroidery, one of the main historic emulsions used in cosmetics and in photographic film, the main coating given to medical capsule pills, and a form of food including jelly, trifle, and marshmallows; the status of gelatin in kashrut is consequently fairly controversial.
Due to the ambiguity over the source of individual items derived from gelatin, many Orthodox rabbis regard it as generally being nonkosher. However, Conservative rabbis and several prominent Orthodox rabbis, including Chaim Ozer Grodzinski and Ovadia Yosef – the former Sephardic Chief Rabbi of Israel – argue that gelatin has undergone such total chemical change and processing that it should not count as meat, and therefore would be kosher. Technically, gelatin is produced by separating the three strands in each collagen fiber's triple helix by boiling collagen in water. Rabbi Dr. David Sheinkopf, author of Gelatin in Jewish Law (Bloch 1982) and Issues in Jewish Dietary Laws (Ktav 1998), has published in-depth studies of the kosher uses of gelatin, as well as carmine and kitniyot.
One of the main methods of avoiding nonkosher gelatin is to substitute gelatin-like materials in its place; substances with a similar chemical behaviour include food starch from tapioca, chemically modified pectins, and carrageenan combined with certain vegetable gums – guar gum, locust bean gum, xanthan gum, gum acacia, agar, and others. Although gelatin is used for several purposes by a wide variety of manufacturers, it has started to be replaced with these substitutes in a number of products, due to the use of gelatin also being a significant concern to vegans and vegetarians.
Today manufacturers are producing gelatin from the skins of kosher fish, circumventing many of these problems.
One of the main biblical food laws forbids consuming blood on account of "the life [being] in the blood". This ban and reason are listed in the Noahide Laws and twice in Leviticus as well as in Deuteronomy. The Priestly Code also prohibits the eating of certain types of fat (chelev) from sacrificial land animals (cattle, sheep, and goats), since the fat is the portion of the meat exclusively allocated to God (by burning it on the altar).
The classical rabbis argued that, in a number of cases, only if it is impossible to remove every drop of blood, the prohibition against consuming blood was impractical, and there should be rare exceptions: they claimed that consuming the blood that remained on the inside of meat (as opposed to the blood on the surface of it, dripping from it, or housed within the veins) should be permitted and that the blood of fish and locusts could also be consumed.
To comply with this prohibition, a number of preparation techniques became practiced within traditional Judaism. The main technique, known as melihah, involves the meat being soaked in water for about half an hour, which opens pores. After this, the meat is placed on a slanted board or in a wicker basket, and is thickly covered with salt on each side, then left for between 20 minutes and one hour. The salt covering draws blood from the meat by osmosis, and the salt must be subsequently removed from the meat (usually by trying to shake most of it off and then washing the meat twice) to complete the extraction of the blood. The type of salt used in the process is known as kosher salt.
Melihah is not sufficient to extract blood from the liver, lungs, heart, and certain other internal organs, since they naturally contain a high density of blood, and therefore these organs are usually removed before the rest of the meat is salted. Roasting, on the other hand, discharges blood while cooking, and is the usual treatment given to these organs. It is also an acceptable method for removing blood from all meat.
Of the rules appearing, in two groups, in Exodus, most do not express dietary laws, but one of the few dietary rules it does list is a ban on eating the meat from animals which have been "torn by beasts"; a related law appears in Deuteronomy's law code, totally prohibiting the consumption of anything that has died from natural causes, and even giving away or selling such things. The Book of Ezekiel implies that the rules about animals which die of natural causes, or are "torn by beasts", were adhered to only by the priests, and were intended only for them; the implication that they did not apply to, and were not upheld by, ordinary Israelites was noticed by the classical rabbis, who declared "the prophet Elijah shall some day explain this problematic passage".
Traditional Jewish thought has expressed the view that all meat must come from animals which have been slaughtered according to Jewish law. These strict guidelines require the animal be killed by a single cut across the throat to a precise depth, severing both carotid arteries, both jugular veins, both vagus nerves, the trachea and the esophagus, no higher than the epiglottis and no lower than where cilia begin inside the trachea, causing the animal to bleed to death. Orthodox Jews argue that this ensures the animal dies instantly without unnecessary suffering, but many animal rights activists view the process as cruel, arguing that the animal may not lose consciousness immediately, and activists have called for it to be banned.
To avoid tearing, and to ensure the cut is thorough, such slaughter is usually performed by a trained individual, with a large, razor-sharp knife, which is checked before each killing to ensure that it has no irregularities (such as nicks and dents); if irregularities are discovered, or the cut is too shallow, the meat is deemed not kosher. Rabbis usually require the slaughterer, known within Judaism as a shochet, to also be a pious Jew of good character and an observer of the Shabbat. In smaller communities, the shochet was often the town rabbi, or a rabbi from a local synagogue, but large slaughterhouses usually employ a full-time shochet if they intend to sell kosher meat.
The Talmud, and later Jewish authorities, also prohibit the consumption of meat from animals who were slaughtered despite being in the process of dying from disease; but this is not based on concern for the health of the eater, instead being an extension of the rules banning the meat from animals torn by beasts, and animals which die from natural causes. To comply with this Talmudic injunction against eating diseased animals, Orthodox Jews usually require that the corpses of freshly slaughtered animals are thoroughly inspected. There are 70 different traditional checks for irregularities and growths; for example, there are checks to ensure that the lungs have absolutely no scars, which might have been caused by an inflammation. If these checks are passed, the meat is then termed glatt (גלאַט), the Yiddish word meaning smooth.
Compromises in countries with animal cruelty laws that prohibit such practices involve stunning the animal to lessen the suffering that occurs while the animal bleeds to death. However, the use of electric shocks to daze the animal is often not accepted by some markets as producing meat which is kosher.
In rabbinical interpretation a continuing application of the commandment is identified. Rabbi Yosef Karo Shulchan Aruch Yoreh Deah 61:1, rules that after the slaughter of animal by a shochet (kosher butcher), the cuts of the foreleg, cheek and maw should be given to a kohen freely, without the kohen paying or performing any service. This giving is required to be free of both monetary and servicial compensation (B.Bechorot 27a).
These gifts are entirely mundane ("chullin") and are not associated with all or part of the sacrificial offerings brought on the central altar in the Jerusalem temple (Mishna Chullin Ch. 10:1). Some chazal opinions maintain that consumption of the animal is forbidden before these gifts are given but halacha rules that although one may consume the meat before the gifts are given it is preferred to ensure the gifts are given prior to consumption. Furthermore, the actual foreleg, cheeks and maw of all kosher-slaughtered beef is forbidden to a non-kohen unless the kohen permits
The classical rabbis prohibited any item of food that had been consecrated to an idol or had been used in the service of an idol. Since the Talmud views all non-Jews as potential idolaters, and viewed intermarriage with apprehension, it included within this prohibition any food which has been cooked or prepared completely by non-Jews. (Bread sold by a non-Jewish baker was not included in the prohibition.) Similarly, a number of Jewish writers believed food prepared for Jews by non-Jewish servants would not count as prepared by potential idolaters, although this view was opposed by Jacob ben Asher.
Consequently, modern Orthodox Jews generally believe wine, certain cooked foods, and sometimes even dairy products, should be prepared only by Jews. The prohibition against drinking non-Jewish wine, traditionally called yayin nesekh (literally meaning "wine for offering [to a deity]"), is not absolute. Cooked wine (Hebrew: יין מבושל, yayin mevushal), meaning wine which has been heated, is regarded as drinkable on the basis that heated wine was not historically used as a religious libation; thus kosher wine includes mulled wine, and pasteurised wine, regardless of producer, but Orthodox Judaism regards other forms of wine as kosher only if prepared by a Jew.
Some Jews refer to these prohibited foods as akum, an acronym of Ovde Kokhavim U Mazzaloth (עובדי כוכבים ומזלות), meaning "worshippers of stars and planets". Akum is thus a reference to activities which these Jews view as idolatry, and in many significant works of postclassical Jewish literature, such as the Shulchan Aruch, it has been applied to Christians in particular. However, among the classical rabbis, there were a number who refused to treat Christians as idolaters, and consequently regarded food which had been manufactured by them as being kosher; this detail has been noted and upheld by a number of religious authorities in Conservative Judaism, such as Rabbi Israel Silverman, and Rabbi Elliot N. Dorff.
Conservative Judaism is more lenient; in the 1960s, Rabbi Israel Silverman issued a responsum, officially approved by the Committee on Jewish Law and Standards, in which he argued that wine manufactured by an automated process was not "manufactured by gentiles", and therefore would be kosher. A later responsum of Conservative Judaism was issued by Rabbi Elliot N. Dorff, who argued, based on precedents in 15th-19th century responsa, that many foods, such as wheat and oil products, which had once been forbidden when produced by non-Jews were eventually declared kosher. On this basis he concluded wine and grape products produced by non-Jews would be permissible.
For obvious reasons, the Talmud adds to the biblical regulations a prohibition against consuming poisoned animals. Similarly, the Yoreh De'ah prohibits the drinking of water, if the water had been left overnight and uncovered in an area where there might be serpents, on the basis that a serpent might have left its venom in the water. In a place where there is no suspicion of snakes, this prohibition does not apply (tosafos, beitzah 6a).
Three times the Torah specifically forbids "seething" a young goat "in its mother's milk" (Exodus 23:19, Exodus 34:26, and Deuteronomy 14:21). The Talmud interprets this as a general prohibition against cooking meat and dairy products together, and against eating or deriving any benefit from such a mixture. To help prevent accidental violation of these rules, the modern standard Orthodox practice is to classify food into either being meat, dairy, or neither; this third category is more usually referred to as parev from the Yiddish word parev (פארעוו) (also spelled parve and pareve) meaning "neutral". As the biblical prohibition uses the word "Gedi" and not "Gedi Izim", the flesh of all "Behemoth" (domestic mammals) is categorised as "meat", while that of fish and bugs is considered parve; however, rather than being considered parve, the flesh of birds and "chayot" (like deer) has been regarded by halakha (Jewish law) as meat for over 2000 years, though only by Rabbinic decree.
One of the major dietary laws that observant Jews keep of Kashruth is that dairy and meat may not be eaten at the same meal. Though it is mentioned many times in the Old Testament, Rashi held that it was connected to two major ethical laws in the Jewish heritage from the original Five Books of Moses, which are, first, to respect the mother animal: Exodus 23:19 "You shall not boil a kid in its mother's milk"; and, secondly, Deuteronomy 22:6 "If you come across a bird's nest beside the road, either in a tree or on the ground, and the mother is sitting on the young or on the eggs, do not take the mother with the young." Some held these relate to the "hurt to living" (tzaar baalei chaim) statute cited throughout Jewish law, against hurting any living thing, the Mishnah Avoth 1:12, "Be a disciple of Aaron... and love all of God's animals" (chaim, living); also, "His compassion is over all of His creatures" (Psalms 145:9) and again the term is chaim, living things.
The Talmud and Yoreh Deah suggest that eating meat and fish together may cause tzaraath. Strictly Orthodox Jews thus avoid combining the two, while Conservative Jews may or may not.
The laws of kashrut can be broken for pikuach nefesh, i.e. when human life or health is at stake. So, for example, it is allowed for a patient to eat non-kosher food if it is essential for recovery, or when one would starve if not partaking of non-kosher food.