Three-star caviar

Once upon a time, before it became so expensive, chefs used to cook with caviar. In Russia, it was mixed with sauerkraut or served with pike as a breakfast dish. One old recipe describes beating it into a butter sauce to accompany a roast cushion of veal.

Low-grade caviar containing mushed eggs (sometimes sold today as pressed caviar) was also used to clarify bouillon. The protein, like the albumen of egg white, helped to precipitate the minute particles suspended in a broth.

Nowadays, however, it's only elite restaurants that can aspire to cook with caviar. Costing upwards of 60p per gram, it's a true luxury and, owing to its increasing scarcity, one that not even chefs in the top flight restaurants can afford to waste.

Paradoxically, caviar is worth serving only if you don't skimp on it. A teaspoon of Beluga on a blini may make a tasty canapé, but it would be an irrelevance to most starters.

When Gordon Ramsay puts caviar in a recipe, it's there for a purpose - and in a quantity that cannot be missed. As the old saying goes, if you've got it, flaunt it. When serving caviar as part of a composite entrée, don't skimp on it or the customer will feel that he's being conned. In Ramsay's starter - tartare of scallops and Oscietra - there's about 25g Oscietra per serving with a food cost approaching £20.

The single most important rule about putting caviar into a sauce (as in the steamed bass fillet with Sevruga velouté recipe) is: "Warm it through, but don't cook it." You add it at the very last moment and you serve it. Left in the sauce, the grains harden and both the taste and texture become unpleasant.

Tasting caviar

Freshness as opposed to fishiness is critical. When a chef tastes a sample, he should put a coffee spoon of caviar on the back of his hand just behind the thumb joint, eat caviar, rub the spot clean and then smell the spot where the caviar was. If there is no residual fishy odour the caviar is of good quality.

Beluga: You can tell it by the tiny "eyes" on each grain - not really for cooking.

Sevruga: Charcoal grey to black, more salty and strongly-flavoured.

Oscietra family: Oscietra is generally grey-brown, smaller-grained, less salted and a "chef's" caviar.

It is also available as Imperial (larger-grained and quite pale) and as Royal Black (similar in colour to Beluga, but from younger Oscietra).

Chefs should also sample pressed caviar, made from second-quality eggs, partially dried. It can be used as a flavouring.

Which caviar?

According to Jean-Pierre Esmilaire of London's Caviar House, Beluga caviar imports to the UK last year accounted for 2% of the market, but its sales account for 20%. His point illustrates one thing: a lot of funny business is going on. Ramsay confesses that unsolicited "caviar sellers" knock on his door about twice a month - and more often than that after he cooked a much-publicised dinner for the Russian President Vladimir Putin at Downing Street.

The chef who buys from a dubious source risks buying a product which is stale or oxidised, which may have been pasteurised more than once, or which may have come from polluted water. The eggs may be soft to the point of mushy, their smell unpleasantly "fishy".

There are more than 25 different grades of Caspian caviar. They come from three kinds of sturgeon. Beluga a carnivorous fish, provides the largest, most expensive eggs, but they aren't ideal for cooking purposes. Oscietra and Sevruga sturgeons are both bottom-feeders, living on plankton and algae. There are two spawning seasons, spring and autumn, so the best produce comes on the market between April and June and September and Christmas.

Ramsay's supplier, Ramin Rohgar of Imperial Caviar (UK), claims that the best Oscietra is available in the spring and the best Sevruga in autumn.

When Escoffier wrote his Guide Culinaire around 1900 most caviar came from Russia. It contained from 8% to 12% salt and, to modern consumers would have been unpalatable. The brackish character of the product explains why chefs mixed capers and chopped onion or lemon with it (a practice Escoffier himself criticised).

Salt reduction began in the 1950s when Iran started exporting. The salt content has dropped now to between 2% and 4%. The term "Malossol" on the label is not a sign of quality, so much as an indication of a low saltiness. Iranian processors also add 2% borax, both as a preservative and to fix the colour of the eggs.

Esmilaire believes that two-thirds of caviar's taste is lost through pasteurisation. If you add a pasteurised product to a sauce or, for example, to Ramsay's scallop tartare, the eggs' subtlety would be lost and the dish would become a pointless extravagance.