Jewish dietary laws are very closely tied in with their religious laws, which were designed to unite a group of tribes, give them a common identity, and to make them different from all those around them.
Just as the Jews kept themselves distinct, they too tried to keep other things in the world distinct from each other. Leviticus 19:19 says “Thou shalt not sow thy field with mingled seed” (i.e. both wheat and barley.) Clothes couldn’t be made of both wool and linen, only one fabric could be used. The ban on “boiling a kid in its mother’s milk”, mixing meat with milk, is another example of keeping things distinct; some have surmised it may be the dietary equivalent of the sexual restriction on incest.
There are 5 classes of food in the Jewish Kosher world:
- Kosher for Passover (extra strict)
- Forbidden (“traif”)
Meat and dairy dishes cannot be eaten at the same meal.
Pareve describes a food which is classed as neither meat nor dairy. It can be eaten at the same time as either meat or dairy. For instance, bread in which vegetable oil was used as the fat, instead of butter.
There are also foods which are forbidden to eat, period.
The prohibition on eating pork is real, but the pig was mentioned as part of a list of other things not to eat. Only later would it be singled out from the list to be something *really* not to eat. Nowadays, we read back into history, and assume that the pig was banned for food safety reasons (e.g. avoiding trichinosis parasites possibly in the meat.) This, however, is reading back into history: there’s no reason to assume that the Jews would have any reasons for thinking along those lines. They certainly weren’t more medically advanced than neighbouring civilisations such as the Egyptians and Greeks: they didn’t even have doctors. The Bible just says, in Leviticus 11:7, that it’s banned because it “cheweth not the cud.” That’s the only reason God gave them — there were no health reasons, and they never pretended there were any.
Strictly kosher-observant Jews won’t eat any beef from a cow that comes from the hindquarters, which is pretty much from the rib-cage back. That means no T-bone steaks, no rib roasts, no filet mignon. The hindquarter can be made kosher if the sciatic nerve is removed: it’s a large nerve fiber that starts in the back of the animal and runs down its hind limbs. As this is a very exacting and time consuming procedure, kosher butchers will usually just sell that hindquarter to a non-kosher butcher.
Seafood or fish must have fins and scales to be Kosher.
Kosher laws can be broken only if it is a matter of physical survival.
A study done by Faye Clark Marketing & Communications, Inc. in 2002 estimated that in Canada, in 2001, only 45% of Kosher goods were bought by Jews. The remaining 55% were bought by consumers who felt that Kosher meant the food was safer or better, or for health and diet reasons (e.g. could be trusted not to contain dairy when it wasn’t supposed to, could be trusted not to contain any animal product when it wasn’t supposed to, etc. 
Kosher for Passover
You can’t use grain flour during Passover: “And this day shall be unto you for a memorial; and ye shall keep it a feast to the LORD throughout your generations; ye shall keep it a feast by an ordinance for ever. Seven days shall ye eat unleavened bread; even the first day ye shall put away leaven out of your houses: for whosoever eateth leavened bread from the first day until the seventh day, that soul shall be cut off from Israel. And in the first day there shall be an holy convocation, and in the seventh day there shall be an holy convocation to you; no manner of work shall be done in them, save that which every man must eat, that only may be done of you. And ye shall observe the feast of unleavened bread; for in this selfsame day have I brought your armies out of the land of Egypt: therefore shall ye observe this day in your generations by an ordinance for ever.” (Exodus 12 : 14 – 17)
Rabbis defined five grains that could ferment or be leavened: barley, oats, rye, spelt and wheat. When corn [maize] from the New World was discovered, they added this to the list.
Jews will use matzo flour (finely ground-up matzohs) instead of wheat flour, which can be a bit hard for an outsider to understand given that matzoh is made of wheat. But matzo flour, as an already cooked food item, can’t be leavened for bread. Very finely ground matzoh flour is called matzo cake meal.
Potato starch is used during this time instead of corn starch.
Yeast is also forbidden, though some people cheat and use a chemical leavener such as baking soda. You can use egg whites, though, to make baked goods rise.
Food that is Kosher must be processed so that it does not come into contact with forbidden foods (such as pork or shellfish), and is not mixed in forbidden ways (such as meat and dairy.) Equipment used must also be separate.
The market for certified Kosher products emerged as food processors because mixing and matching their ingredients. You might think what could not be Kosher about a tin of carrots, but the processing equipment used could also have been used to make Pork and Beans. Pickles for instance, as vegetables, would naturally be Kosher, so you might think why are there Kosher pickles, wouldn’t all pickles would be Kosher? Sometimes, though, materials derived from animals such as animals might be used in the brine as an emulsifier, which would mean the pickles couldn’t be served at the table with dairy courses. The United States Department of Agriculture (USDA), allows products that use up to 1% meat fat to still label themselves as having used 100% vegetable shortening. Coca-Cola has been certified kosher, as well as kosher for passover, since 1935.
There are many Kosher certifying organizations. The Union of Orthodox Jewish Congregations (UOJC) in New York City is the largest certifier in America. The food processors pay the UOJC to have Kosher inspectors, and sometimes Rabbis (for cheese, for instance, because rennet is used to curdle many cheeses, and rennet is an animal product) come and inspect their processes so that they can put the marks on their goods.
There are well over 25 symbols used in various countries:
- The U symbol in a little circle is issued by “The Union of Orthodox Jewish Congregations of America”;
- The K symbol in a little circle is issued by the “The Organized Kashrus Laboratories”;
- In Canada, a mark is MK (standing for Montreal Kosher) issued by the Jewish Community Council of Montreal ;
- Another mark in Canada is COR, issued by the “Kashrus Council of Canada”;
- In the UK, Kosher certification is issued by Kedassia – The Joint Kashrus Committee of England or Manchester Beth Din;
- Other symbols in America include OU, OK, Star K, Chof K, etc.
Kosher does not necessarily mean the food is healthier: anyone Jewish would guffaw at the idea of traditional Jewish food such as a plate of Latkes, Blintzes or Knishes being healthy.
The Kosher dietary laws are derived from the Old Testament of the Bible (specifically Leviticus and Deuteronomy). The laws are very complicated, and Jews will spend the rest of eternity debating them. There is no agreement between difference branches of Judaism. Some discard some of the older dietary laws, some Jews seek new ways in which to keep Kosher. Many people try to come up with rationalizations for the various laws, but all of this is just reading modern knowledge back into history. The actual religious laws don’t give a reason; they just say “do it”. Special, more restrictive Kosher rules apply to Passover.
Literature & Lore
“AMERICAN canners have entered a new field. They are producing canned foods which are kosher foods.
For a long time the orthodox Jew has recognized the value of using canned foods both because of the saving in time and money, and because of the superior quality of the food. But religious scruples deterred him. How could he be sure that such food had been prepared in a manner which followed his law?
At last a board was organized, and the ‘Official Corporate Seal of the Rabbinical Board’ on canned foods bears its mute testimony, assuring the Hebrew that this partioular food is approved.
Products of different companies have been approved as kosher, and there are now many foods canned, especially for the Jewish trade. The labels of the cans are in both English and in Yiddish. On one side is the English label and directions. On the other is something like this: ‘Tongue, Smoked and Cooked, a Delightful Bite’, and the follows the manufacturer’s name. The certificate of the Rabbinical Board is givein in English and Yiddish, and in both languages are the directions to ‘Open can, to be sliced and served hot or cold’. Besides oxtongue, there are sausages, frankfurters, goulash, pastrama, tongues, beef fat and baked beans.
Development of this phase of the canning industry is only another example of the interest taken by canners in the wants of special groups.” — Kosher Food Comes in Cans. Olean, New York: The Olean Evening Times. Monday, 19 December 1927. Page 11.
Kosher, though it looks like a Yiddish word, comes from the Hebrew “kasher”, meaning “clean, fit, proper.” Also spelt “Kashruth” and “Kashrut.”
 Faye Clark Marketing & Communications, Inc. Canada Kosher Foods Latest Trends in Kosher Foods 2002.