Cognac obtains its, golden brown colour from contact with natural vesins during its time reposing in oak barrels. The natural evaporation, called "Angels share" is necessary to acheive a perfect product. The oak trees of the forest of Limousin and Tronçais provide the only wood suitable for the construction of the barrels.
After ageing for two or three years the eau-de-vie is mature enough to be drunk. But o longer period required to improve its qualities. Bouquet, delicacy and mellowness os taste reach their peak after 20 years.
The classifiction of Cognacs depends an their age :

==> *** et V.S. : less of 4 years ½.
==> V.S.O.P. (Very Special Old Pale) : 4 years ½ minimum.
==> V.O. (Very Old) : 5 years ½ minimum.
==> X.O., Napoléon, Extra, Hors d'age : 6 years ½ minimum.

Note :
The appellation "Fine Champagne" is awarded only to Cognac blended from the eau-de-vie produced in the "Grand Champagne" (50 % minimum) and the "Fine Champagne".