This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
True cognac or wine oil, ten parts; ethyl acetate, 100 parts; raisin extract, 100 parts; alcohol, 1000 parts. This formula (if the true cognac oil is used) furnishes a superior product, and is usually rectified.
The addition of some of these essences to diluted alcohol will furnish an imitation of cognac, provided all the ingredients are what they pretend to represent and pure. The quantities to be employed are varying. From one quart of the essence and upwards is usually used to prepare a barrel of twenty-five gallons. Probably the best possible imitation of cognac is produced as follows: Mix seventy-five grains of pure oenanthic ether with twenty-five gallons of diluted alcohol. The latter must be perfectly deodorized, as it is a fact that impure or carelessly purified alcohol considerably impairs the remarkable properties of this ether, and extensively reduces the aroma of the imitation product. Color, if desired, with some curcuma extract or sugar-color slightly yellow, fill all the liquid in bottles, and put them in water and heat (in the same way as beer is Pasteurized) to 60 or 70° C. (140° to 158° F.) for fifteen minutes. Then let slowly cool. By this process the cognac becomes "aged," and a product is obtained that hardly differs from the natural product.