Kosher refers to that which is prepared in accordance with Jewish law. Kosher foods are foods that practicing Jews are allowed to consume. The specific rules are enumerated in the Torah, and refined in the Talmud.
There are two groups of rules - what can be eaten and how it can be prepared.
If you want to keep things simple, serve a vegetarian meal that excludes either dairy or eggs.
What can be eaten
- Any fish that has both scales and fins. This means that shellfish are not kosher, and neither are fish like catfish.
- Any land animal that chews its cud and has split hooves. Sheep and cows are kosher animals, while pigs, horses, and dogs are not kosher. Pigs do have a split hoof, but they do not chew their cud, so they are not kosher. Both deer and goats are kosher if properly slaughtered. There are also restrictions as to what parts of the animal may be eaten. Some parts may never be eaten and some are not normally processed as kosher meat in the United States, due to the additional labor involved. Kosher hot dogs cannot contain some of the filler and miscellaneous scraps that are added to most non-kosher hot dogs.
- The Torah contains a list of non-kosher birds, predominantly scavengers and predators. Kosher birds include duck, chicken, and turkey. Ostrich is not kosher.
- There are some kosher insects, types of grasshopper or locust. Ashkenazi and most Sephardi groups have lost the tradition of which exact species are kosher, but Yemenites and some Mizrachi groups have maintained this tradition and can properly identify them (though to most Westerners the prospect of eating insects is not appealing, rendering this a largely academic point).
- There is a special, more strict set of rules for the period of Passover that excludes most wheat products and yeast. The Ashkenazi community also forbids rice, corn, and bean during this time.
- No blood of any kind is to be eaten.
- Eggs from kosher birds are kosher. Eggs are not used if any blood spots are found.
- Honey made by bees is kosher even though it is processed by a non-kosher insect.
- An animal that is sick or injured cannot be eaten. Roadkill is not kosher.
- All kosher animals must be slaughtered properly in order for the meat to be permissible.
- There are some restrictions on plants. They must be checked for insects.
- Any beverages made from grapes, including grape juice and wine, require special processing and supervision to be kosher.
- Gelatin is usually made from nonkosher animals' hooves or bones, but it is possible to get kosher gelatin either made from kosher fish, kosher animals or vegetable products.
- Ask a local rabbi or kosher organization for more details.
How it can be prepared
- It is not enough for an animal to be kosher; the animal must also be slaughtered in a specific way as to minimise the amount of pain it feels.
- Meat must be "kashered", which removes the blood from the meat. This is done either by salting or roasting. Most kosher meat that one can buy is already kashered.
- Milk and meat cannot be cooked or eaten together. This includes eating dairy and meat within certain time periods. Depending on the family's custom, this is over 5 hours or 3 hours before consuming dairy products after meat products. Some hold that it is permissible to wash out your mouth before consuming meat products after dairy products, except for aged cheese, which requires the same waiting period as is required to eat dairy after meat. One must have two entirely different sets of cooking pots and table dishes for milk and meat. Both birds and mammals are considered meat, while fish, insects, and eggs are considered to be neither dairy or meat. Fish can be eaten with meat or dairy, although some hold that one should not eat fish and meat off of the same dish. Some Jews of Sephardic backgrounds follow Maimonides' ruling, and do not mix fish with dairy products of any kind.
The U or K within a circle are two of many symbols used by Jews in the USA to identify kosher products. A "plain k" [a K all by itself] does not mean that the food is certified kosher, but rather that the company declares it to be kosher. Many Jews do not accept "plain k" as a legitimate kashrut certification.
A list of many of the kosher certification agencies are found here: http://www.kashrut.com/agencies/
Some Jews will not accept certain certifications, as interpretations and levels of observance vary from Jew to Jew.
- If you are entertaining for people that you know or think may keep kosher, be sure to ask them about their personal rules, as there are many interpretations and subtle variations. Depending on their observance, they may be fine eating a vegetarian dish cooked in your home, or may not be comfortable doing anything more than eating unprepared fruit. Strict Kashrut includes categorizing the cooking vessels, the serving containers, the cutlery and the cooking surfaces as kosher or non-kosher as well. Generally, if a pot has been previously used to cook non-kosher meat, one cannot use it to produce a kosher meal.
- Here is a more detailed explanation of Kashrut.
Union of Orthodox Congregations, the largest kosher-certification organisation in the USA and other places worldwide.