It is significant that one of the first commandments given to human beings concerned food. Adam and Eve were told not to eat the fruit of the Tree of Life. Ever since, Jews have always placed great emphasis on gastronomic self-control.

The main principles of Kashrut are laid down in the Five Books of Moses and are classified as "statutes" - no reason is given for keeping them other than we are commanded to do so. Nevertheless Rabbis have always stressed their essential role in preserving Jewish life.

By keeping Kosher, children from an early age learn discipline, distinguishing between what is permitted and what is not. Beyond the exercise of self-restraint, the Rabbis in the Talmud came up with another, more mystical idea. If you eat non-kosher food, they said, it reduces your spiritual capacity - "clogs up the pores of your soul."

Just as a healthy diet is good for the body, so we keep kosher because it's good for the soul. In the Jewish home, the table is an altar, the kitchen is a domestic sanctuary.

MEAT & MILK
Central to maintaining a kosher lifestyle is the separation of meat from milk. The prohibitions against mixing them are very strict, in some respects more so than other Kashrut regulations.

For example, you can't eat crocodile because it's not kosher but you can wear crocodile-skin shoes. But you are not allowed to derive any benefit at all from the mixture of meat and milk. So while Jews are allowed to work as chefs in non-Jewish restaurants (provided of course they don't taste the food), they may cook the burgers, but not the cheeseburgers.

Some people are meticulous enough to even check their dogs' or cats' pet food to ensure there is no milk-powder among the ingredients.

This idea of stringent separation explains why it is necessary to have different sets of cutlery, crockery, cooking utensils and washing-up-bowls for meat and dairy meals. A dishwasher should be used either for meat or milk dishes but not both.

Food that is neither meat nor dairy is called 'pareve' - neutral - and pareve utensils like salad bowls or drinking glasses can accompany both milk and meat meals. Ordinary non-absorbent glass may be designated pareve. But Pyrex and other oven proof dishes glass must be designated either meat or milk.

We not only avoid mixing meat and milk at the table, we also abstain form eating dairy foods after meat until some time has elapsed. The Shulchan Aruch, the Code of Jewish law, actually records two traditions, one of waiting for one hour (which the Dutch still adhere to) and one for six. The prevailing Anglo-Jewish custom is to wait for three. In the case of eating meat after milk, the same interval applies only after eating, hard cheese.

And in order to prevent confusion, bread should always be pareve - so it must not be made with butter or milk.

FISH & MEAT
Another rule is not to eat fish and meat together - but for a different reason to that of meat and milk. It is simply that the Rabbis, advocates of a healthy lifestyle, believed it physically harmful. So you shouldn't use Worcestershire Sauce, which is made from anchovies, in the preparation of a meat dish.

It's perfectly okay to eat meat immediately after fish and vice versa, say a salmon canapé after a cocktail sausage at a reception. But it is the custom to cleanse the palate first by having some bread or a drink. This may explain the reason why many people drink a Le'chaim - a toast in whisky, vodka or another strong liquor - after the gefilte fish at the Shabbat table before moving on to the next course.

MEAT
The basic rules about which animals, birds and fish are kosher are set out in Leviticus chapter 11. As for red meat, the animals must have cloven hooves and chew the cud - such as goats, sheep, cattle and deer.

Venison is no longer available for kosher tables only because, according to agricultural regulations, deer must be shot in the open field, not brought into an abattoir. But in the 19th century, Kosher butchers used to go down to the Rothschilds estate once a year to preserve the tradition of shechting, slaughtering deer in England.

BIRDS
The Torah lists only the birds which are forbidden to eat, such as ostriches, owls and vultures. We cannot be sure however of the true identity of the species listed. But by tradition, we can eat poultry such as duck, chicken goose and turkey, and also pigeon, pheasant and partridge. A Germanic tradition also allows sparrow!

SHECHITA
Kosher meat and poultry must be prepared by the hallowed method of shechitah - a swift cut by a razor-sharp knife - which Jews believe to be the most painless means of slaughtering the animal. After shechitah, the animal must undergo a thorough inspection (bediko) to check if there are any blemishes which according to Jewish law render it unkosher. The lungs of cattle and intestines of chickens are always checked.

This is where the term "glatt kosher" comes in. In the case of cattle, if the lung is free of adhesions, it is termed "glatt" - smooth. If there are adhesions, the animal may still be kosher - though not glatt - provided these leave no hole when they are taken off.

NIKKUR - PORGING
Before the meat reaches the shop counter, there is one more process to undergo - nikur, porging. This entails the removal of a number of veins and forbidden fats. Because porging is so tricky in the hindquarters of an animal, it is not carried out in most Diaspora communities and this part of the animal is sold to the non-Jewish market. The hindquarters, incidentally, contain the sciatic nerve which the bible mentions as shunned by the Children of Israel because it was where Jacob was wounded in his wrestling match with the angel.

MELICHA - SALTING
Finally to be fit for Kosher use, the meat must be drained of any remaining blood - the consumption of which is strictly forbidden by the Torah. That is why it must be soaked and salted before food preparation. Nowadays, most meat is koshered before sale by the butcher, thus sparing the consumer the trouble.

Liver, however, usually does need to be koshered at home and since it is full of blood, it has to be roasted by a naked flame. Maybe chopped liver became popular because it was the best way to serve liver after roasting.

EGGS
Because of the strictures against blood, it is customary to check eggs that have been opened before cooking, so as to reject any with blood spots. There's no requirement, however, to check them before hard-boiling. White eggs on sale commonly have fewer blood spots than brown ones not for any biological reasons: it is simply that in the factory "candling" process, white eggs with bloodspots are easier to detect and thus they are rejected before they reach the shops.

FISH
Whilst there are a few available varieties of kosher meat or poultry, this is not true of fish. The sea's almost the limit. Like television, the fishmonger's counter was once in black and white. Now through all kinds of exotic imported species, it offers a rainbow of choice.

Jews have always had a soft spot for fish - the Israelites even moaning about the absence in the wilderness of the fish they got in Egypt!

To comply with kosher requirements, a fish must have fins and easily detached scales. The scales of a sturgeon are extremely hard to remove - hence it is non-kosher, as is it's precious roe, caviar. All shellfish, eels, shark, monkfish, huss and catfish fail the kosher test. Fresh or frozen fish should be bought with the skin on so you can check the scales.

VEGETABLES
Whereas eating pork involves a single transgression, eating a fly, worm or other kind of creepy-crawly involves several. The Torah is very explicit in its ban on insects so fruit and vegetables liable to be infested with them have to be thoroughly scrutinised and cleansed.

What looks like a nice green lettuce leaf, on closer inspection may resemble insect motel. Other tricky customers are parsley, asparagus, spring greens, broccoli and watercress.

All bugs visible to the naked eye have to be removed: one way is to soak the vegetables in water with a little salt or vinegar. Another method is to buy one of the several brands of vege-cleaner on the market, put some on a sponge and wipe it across the leaf. Insects also, unfortunately, lurk in some canned fruits and vegetables: visible as little black specks, they can be sifted out, using a muslin sheet.

MILK
Since it is not possible to distinguish Kosher milk (ie. Milk from a Kosher animal) from non-kosher milk, rabbinical law requires that milk be supervised from the point of milking until it is bottled in order to guarantee that it comes from a Kosher animal. In countries where the source of milk offered for sale is guaranteed by civil law (such as the UK), some authorities rule that all milk is guaranteed as Kosher and need not be supervised. Supervised "Kosher" milk (Chalav Yisroel) is widely available nowadays in the major centres of Jewish life.

CHEESE
When it comes to cheese, though, the rules are tighter. All cheese must be rabinically certified. This is because the curdling agent, the rennet, is often derived from an animal source - usually a calf's stomach. The Rabbis in the Talmud ruled that all cheese must come from a supervised source, even where the rennet was made from herbs. So vegetarian cheeses cannot be used, unless they have a rabbinic seal.

WINE
Wine and Grape juice likewise must come only from a rabbinically approved source - but not for the same reason as cheese. The Sages put a ban on non-Jewish wine primarily as a safeguard against intermarriage, believing that by drinking-out one might end up dating-out. Hence products like brandy and wine vinegar must also carry a rabbinic seal.

As it happens non-kosher ingredients occur in the manufacture of non-Jewish wines, such as isinglass, a "fining" agent, which comes from a sturgeon - another reason for avoiding them.

BREAD
The Rabbis also discouraged the consumption of bread not manufactured by Jews, though in a place where Jewish manufactured bread is not available, or is of inferior quality, commercially produced non-Jewish bread can be used, subject to the following rider:
Bread usually contains fat, which may be of animal (or unknown) origin. There is also the possibility of an emulsion or glaze being applied to the crust, or of non-kosher fat being used to grease the baking-tins; such fat need not appear on the list of ingredients. Further, the bread may be baked in the same ovens as non-kosher bread or cakes; this too would render it non-kosher.

BISCUITS
They are usually made with non-kosher margarine. Those made with butter may still not be kosher, as tins may be greased with non-kosher fat and no indication of this will appear on the label. Cakes present the same problems. In common with all other cooked products, cakes and biscuits whose own ingredients are perfectly acceptable may be cooked in tins or pans used for non-kosher products or in ovens together with non-kosher products. For these reasons, each item must be considered individually.

MARGARINES
They contain fats and emulsifiers which may be of animal origin; even the manufacturers of "vegetarian" margarine cannot always guarantee that the source of their emulsifier is vegetable. Only margarine under rabbinical supervision can be used.

PROCESSED FOODS
Since the 20th century, Kashrut has had to contend with a whole new challenge: processed foods. Thanks to the efforts of Kosher food technologists, thousands of products on the shelves have been cleared for use by Jewish consumers.

Increasingly, products carry a kosher label - like the KLBD, Kosher London Beth Din logo. Many others have been approved after rigorous inspection of the ingredients and the procedures used in manufacturing them.

Each ingredient and food additive has to be individually checked to ensure it does not derive from a non-kosher source. Many seemingly innocent products, such as yoghurt, may contain gelatine, spices may contain stearic acid salts, and even breakfast cereal may contain glycerine of animal origin.

Even where the ingredients are fine, the product may still be non-kosher because of other unlisted agents used in its manufacture - such as release agents used to grease the production line.

And even when a product is guaranteed vegetarian, it may still be non-kosher if the factory has prepared it on equipment which has been previously used for products containing meat. Thus, with the ever increasing sophistication of food technology. The London Beth Din Really Jewish Food Guide has become an essential handbook for every Really Jewish home.