About 9 litres of wine for 1 litre of eau-de-vie at 72% abv.
It takes 9 litres of wine to obtain 1 litre of eau-de-vie at 72% abv. That means two-thirds of the initial volume is lost with each heating.
The heart of the “bonne chauffe”: 40% of the volume of the brouillis
During the second distillation, the first, most volatile products are discarded. In too high concentration, they would alter the quality of the eau-de-vie. These are the “heads” (“têtes”). They represent 1-2% of the volume of the brouillis.
The next products to appear are much finer and rich in floral aromas. They constitute the “heart” (“coeur”) of the distillation, the future Cognac—about 40% of the volume of the brouillis.
The following portion is called the “secondes”, representing about 30% of the volume of the brouillis. Neither the “secondes” nor the “tails” (“queues”) — the last 10% of the distillate—will be kept.
This separation of the different portions is called “cutting” (“la coupe”).
The remaining volume of the brouillis is composed of residues, which are not distilled.