The eggs must be intact, juicy and whole. Lower quality caviar, in fact, comes from eggs that break while being extracted (at least 35%), which gets pressed and then sold.
Starting from the idea that the clearer the colour, the higher the quality, the four levels of classification are:
0 (very dark colour)
00 (medium tone)
000 (clear shade)
The fourth level is Royal Caviar, which is the best
Salt should be added as little as possible so as not to cover the flavour, although a bit is needed for conservation. The average percentage of salt should be between 4-8%.
This rule should be applied to all kinds and varieties of caviar. Any other ingredient other than caviar and salt is superfluous and should be avoided.