Cognac wines are distilled in Alembic stills of copper, and always twice. When the still is charged the first part of the distillate is collected separately, the “ heart “ goes into barrels, and the tail is run into the collected “ head “ to be redistilled. Cognac is distilled out at 70 per cent alcohol strength and aged in barrels made of aged Troncais or Limousin oak. Both impart different flavours to the end product and producers decide on their style based on wood preference. R. Martin uses Limousin oak, whereas Martell prefers Troncais. The former imparts a rich tannic flavour and ages the brandy faster because of its larger pores!
Cognac barrels hold 500 litres and are stored in warehouses interspersed throughout Charente Maritime, since to date no insurance company has ventured into insuring a huge Cognac warehouse. The risk is too high from evaporating alcohol, which can easily spark an infernal fire that would burn intensely and for weeks.
The evaporation of Cognac at first is about four per cent, which decreases gradually to two per cent. The evaporated volume represents a significant loss, and thus the older the Cognac the more expensive and smoother the Cognac becomes.