Not all caviar comes from sturgeon – red caviar comes from salmon. Traditionally the roe from 4 species of sturgeon was considered to produce the best caviar: the Beluga, Ossetra, Sevruga and Sterlet.
The small golden eggs of the Sterlet sturgeon were the caviar of the Tzars and was the rarest and, at one time the most cherished of all caviar. So insatiable was the Russian nobility's passion for this golden caviar that the species is all but extinct today.
Beluga is the largest of the sturgeon family (they can reach up to 13 ft), produces large, loose, glistening black to steel grey berries, has a walnut flavour. The lighter colours come from older fish, and are the most valued. A pearly white variety, called Almas (Persian for diamond), taken from a centennial female sturgeon, is the rarest type of Beluga .
Ossetra caviar ranges from warm brown to green-gray in color, to dark blue to jet black or even white and the eggs are slightly smaller than the Beluga caviar. The golden eggs, known as Golden Caviar, were favoured by the Shahs of Iran and have a delicate mellow nutty taste.
Sevruga caviar has the smallest eggs within the Caspian Sea and is usually light to dark grey. This caviar has the strongest taste of the sea and salt with a warm, aromatic and savory flavour.