The four main types of caviar are Beluga, Sterlet, Ossetra, and Sevruga. The rarest and costliest is from beluga sturgeon that swim in the Caspian Sea, which is bordered by Iran, Kazakhstan, Russia, Turkmenistan and Azerbaijan.
Caviar, according to the Food and Agriculture Organization, is a product made from salt-cured fish-eggs of the Acipenseridaefamily. The roe can be “fresh” (non-pasteurized) or pasteurized, with pasteurization reducing its culinary and economic value.
Traditionally the term caviar refers only to roe from wild sturgeon in the Caspian and Black Seas (Beluga, Ossetra and Sevruga caviars). Depending on the country, caviar may also be used to describe the roe of other fish such as salmon, steelhead trout, trout, lumpfish, whitefish,and other species of sturgeon.
Caviar spoons are traditionally made of inert materials, especially mother of pearl. There is a custom that caviar should not be served with a metal spoon, because metal may impart an undesirable flavor. Some food experts point out that caviar is stored and sold in metal tins, and therefore any effect of metal on caviar flavor is a misconception;however, others point out that silver is reactive, and may affect caviar flavor.