What are the rules of keeping kosher?

The Rules of Keeping Kosher (Kashrut)

Keeping kosher (kashrut) refers to the system of Jewish dietary laws derived from the Torah and elaborated by the Talmud and rabbinic authorities. At its core, kashrut governs which foods are permitted (mutar), which are forbidden (asur), and how permitted foods must be prepared and combined. The Rambam (Maimonides) captures the spiritual dimension of these laws: "Whoever is careful concerning these matters brings an additional measure of holiness and purity to his soul" [Mishneh Torah, Forbidden Foods 17:32], citing the verse "וְהִתְקַדִּשְׁתֶּם וִהְיִיתֶם קְדֹשִׁים" — "And you shall sanctify yourselves and you will be holy, for I am holy" (Leviticus 11:44).

Key Takeaways

Only certain animals, birds, and fish with specific physical signs are permitted to be eaten.
Meat must be slaughtered in a precise ritual manner (shechita) and salted to remove blood.
Meat and dairy products may never be mixed or eaten together.
Kosher food purchased from unknown sources requires reliable certification or a trustworthy reputation.
Kashrut has both legal (halachic) and spiritual dimensions — it is a system of holiness, not merely hygiene.

I. Permitted and Forbidden Animals

Land Animals

The Torah in Leviticus 11 and Deuteronomy 14 establishes two signs that make a land animal kosher (tahor):

Split hooves (parsah shesusah)
Chewing the cud (maalat geirah)

Both signs must be present. Thus:

✅ Cows, sheep, goats, deer — permitted
❌ Pigs (split hoof but does not chew cud) — forbidden
❌ Camels (chews cud but no split hoof) — forbidden

[Mishneh Torah, Forbidden Foods 1:1–2]

Birds

The Torah lists forbidden bird species by name. The tradition identifies permitted birds as those with the following signs: an extra talon, a crop, and a peelable gizzard. In practice, only birds with an established mesorah (tradition of being eaten) are consumed [Mishneh Torah, Forbidden Foods 1:14].

Commonly permitted birds include chicken, turkey, duck, and goose.

Fish

Fish must have fins and scales (snapir v'kaskeses) to be kosher [Leviticus 11:9].

✅ Salmon, tuna, carp, herring — permitted
❌ Shellfish, shrimp, lobster, catfish — forbidden
❌ All sea mammals — forbidden

Insects

The consumption of insects is strictly forbidden. This has practical implications for checking vegetables and leafy greens for infestation [Mishneh Torah, Forbidden Foods 2:21, which addresses liability even for minute forbidden creatures].

II. Ritual Slaughter (Shechita)

Even a kosher animal species must be slaughtered correctly to be permitted. The slaughter must be performed by a trained, G-d-fearing expert called a shochet.

Key requirements:

A swift, uninterrupted cut across the trachea and esophagus with a perfectly sharp, nick-free blade
No pressure, pausing, or tearing
An animal found to have certain internal defects after slaughter is called treif (technically tereifah) and is forbidden

If an animal is found to be treif after slaughter, it may not be eaten regardless of how it was slaughtered [Mishneh Torah, Paschal Offering 1:20 implies this principle broadly].

III. Removal of Blood

Blood (dam) is forbidden by Torah law [Leviticus 7:26 — "וְכָל דָּם לֹא תֹאכְלוּ" — "And you shall not eat any blood"].

To remove blood, meat undergoes:

Soaking in water for 30 minutes
Salting on all sides with coarse kosher salt for one hour
Rinsing to wash away the blood and salt

Liver, which is blood-rich, requires broiling directly over a flame rather than salting.

IV. Separation of Meat and Dairy (Basar b'Chalav)

One of the most well-known aspects of kashrut is the prohibition of mixing meat and milk, derived from the verse repeated three times in the Torah: "לֹא תְבַשֵּׁל גְּדִי בַּחֲלֵב אִמּוֹ" — "You shall not boil a kid in its mother's milk" [Exodus 23:19; 34:26; Deuteronomy 14:21].

The Rabbis derived three separate prohibitions:

Cooking meat and milk together
Eating them together
Deriving benefit from such a mixture

Waiting Between Meat and Dairy

After eating meat, one must wait before consuming dairy. The standard wait is 6 hours, based on the ruling of Mar Ukva and later authorities [Chullin 105a; Shulchan Arukh, Yoreh De'ah 89:1].
Ashkenazic communities: 6 hours
Some Sephardic communities: 6 hours; others have varying customs (1 hour, 3 hours, or after the meal ends)
After dairy, the wait before meat is shorter — one need only rinse the mouth and eat a bite of pareve food, though hard cheeses require a longer wait.

Separate Utensils

Separate dishes, pots, and utensils must be maintained for meat (fleishig) and dairy (milchig). A third category, pareve, refers to neutral foods (eggs, fish, vegetables) that may be eaten with either.

V. Wine and Certain Processed Foods

The Rambam rules that wine, meat, cheese, and fish without obvious signs require reliable sourcing:

"Nowadays, in all places wine is not taken from anyone without such a reputation [for keeping kashrut]. And so it is with regards to meat, cheese and fish without obvious signs." [Mishneh Torah, Forbidden Foods 11:25]

Yayin Nesech (Wine Touched by Non-Jews)

Wine handled by non-Jews (stam yeinam) has a complex set of rabbinic restrictions. Most authorities forbid drinking such wine [Yoreh De'ah 123–124].

Trusting a Host

The Rambam rules that when one is a guest in a Jewish home, no further investigation is needed into the kashrut of the food — unless the host is known to be lax in observance:

"If, however, [the host] is reputable for not upholding the laws of kashrut...it is forbidden to be a guest in his house." [Mishneh Torah, Forbidden Foods 11:26]

VI. Kosher Certification (Hashgacha)

In the modern era, the purchase of processed and packaged foods requires reliable hashgacha — rabbinic supervision. This is the practical application of the Rambam's ruling that food from unknown sources requires a trustworthy reputation [Mishneh Torah, Forbidden Foods 11:25].

A certified kosher product bears a hechsher (kosher symbol) from a recognized rabbinic authority.

VII. The Spiritual Dimension

The Rambam closes his laws of forbidden foods with a powerful statement:

"Whoever is careful concerning these matters brings an additional measure of holiness and purity to his soul and purges his soul for the sake of the Holy One, blessed be He." [Mishneh Torah, Forbidden Foods 17:32]

The Sefer HaChinuch (Mitzvah 73) explains that kashrut purifies the mind and character. Nachmanides (Ramban) on Leviticus 11 emphasizes that forbidden foods coarsen the soul, while permitted foods keep it refined.

Kashrut is thus not merely a system of physical health or ethnic identity — it is a