Kosher : Special Diets
Kosher refers to that which is prepared in accordance with Judaic 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.
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 a split hoof. Sheep and cows are kosher animals, while pigs and horses and dogs are not kosher. Pigs do have a split hoof, but they do not chew their cud, so they are not kosher. There are also restrictions as to what parts of the animal may be eaten. (kosher hot dogs cannot contain some of the filler and miscellaneous scraps that are added to most non-kosher hot dogs)
There is a list of non kosher birds in the Torah, which names predominantly scavengers and predators. Kosher birds include duck, chicken, and turkey. Ostrich is not kosher.
There are some kosher insects that are types of grasshopper or locust. Ashkenazi and most Sepharadi groups have lost the tradition of which exact species are kosher, but Yemenites and some Sepharadi groups have maintained this tradition and can properly identify them (though to most people the prospect of eating insects is not appealing, rendering this a largely academic point).
Animal blood is not to be eaten.
An animal that is sick or injured cannot be eaten.
There are no restrictions on plants.
Gelatin is usually made from non kosher animal’s hooves/bones, but it is possible to get kosher gelatin.
How it can be Prepared
It is not enough for an animal to be kosher, that animal must also be slaughtered in a specific way as to minimise the amount of pain dealt to the animal.
Meat must be “koshered”, which removes the blood from the meat. This is done either using kosher salt or broiling. Most kosher meat that one can buy is already koshered.
Milk and meat cannot be cooked together. To be on the safe side, traditionally Jews do not eat dairy and meat in the same meal, and usually delay for 3 hours before consuming milk or milk products after meat. Both birds and animals are considered meat, while fish and insects are considered to be neither dairy or meat. This catergory is called parve.
Store Bought Goods
Ever wonder what the U with a circle? Or that little K? Well those are two of many symbols used by organisations to show that they approve that a product is Kosher. But a solitary K does not mean that the food is kosher but the company declares it to be kosher. There are lots of signs for example a kof with a K in it is a sign too.
Notes
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 that different people will follow.
A more detailed explanation of Kosher