Cognac origineCognac production falls under French appellation d'origine contrôlée designation, with production methods and naming required to meet certain legal requirements. Among the specified grapes, Ugni blanc, known locally as Saint-Emilion, is most widely used. The brandy must be twice distilled in copper pot stills and aged at least two years in French oak barrels from Limousin or Tronçais. Cognac matures in the same way as whiskies and wines barrel age, and most cognacs spend considerably longer "on the wood" than the minimum legal requirement.
GrapesThe white wine used in making cognac is very dry, acidic, and thin. Though it has been characterized as "virtually undrinkable", it is excellent for distillation and aging. It may be made only from a strict list of grape varieties. For it to be considered a true cru, the wine must be at least 90% Ugni blanc (known in Italy as Trebbiano), Folle blanche and Colombard, while up to 10% of the grapes used can be Folignan, Jurançon blanc, Meslier St-François (also called Blanc Ramé), Sélect, Montils, or Sémillon. Cognacs which are not to carry the name of a cru are freer in the allowed grape varieties, needing at least 90% Colombard, Folle blanche, Jurançon blanc, Meslier Saint-François, Montils, Sémillon, or Ugni blanc, and up to 10% Folignan or Sélect.
Fermentation and distillationAfter the grapes are pressed, the juice is left to ferment for 2-3 weeks, with the region's native, wild yeasts converting the sugar into alcohol; neither sugar nor sulfur may be added. At this point, the resulting wine is about 7 to 8% alcohol.
Distillation takes place in traditionally shaped Charentais copper alembic stills, the design and dimensions of which are also legally controlled. Two distillations must be carried out; the resulting eau de vie is a colourless spirit of about 70% alcohol.
Once distillation is complete, it must be aged in Limousin oak casks for at least two years before it can be sold to the public. It is typically put into casks at an alcohol by volume strength around 70%. As the cognac interacts with the oak barrel and the air, it evaporates at the rate of about 3% each year, slowly losing both alcohol and water. This phenomenon is called locally la part des anges, or "the angels' share". When more than ten years pass in the oak barrel, the cognac's alcohol content decreases to 40% in volume. The cognac is then transferred to "large glass bottles called bonbonnes", then stored for future "blending." Since oak barrels stop contributing to flavor after four or five decades, longer aging periods may not be beneficial.
The age of the cognac is calculated as that of the youngest component used in the blend. The blend is usually of different ages and (in the case of the larger and more commercial producers) from different local areas. This blending, or marriage, of different eaux de vie is important to obtain a complexity of flavours absent from an eau de vie from a single distillery or vineyard.