doubler, thumper, keg, and retort are all terms for a reflux chamber inserted between the still and the condenser to perform what is in effect a second distillation (hence the American term, “doubler”). It usually takes the form of a cylindrical chamber with the vapor pipe from the still entering through the top and running almost to the bottom of the chamber. Vapor enters from the still and expands to fill the chamber, allowing reflux to occur and water and other heavier compounds to condense. As these build up, they soon rise above the mouth of the inflow pipe, and the incoming vapor then bubbles through the liquid, leaving behind more condensate and taking any alcohol that has remained behind with it through an exit pipe to the condenser. Usually there is a third pipe leading back to the still so any excess condensate can be redistilled.
In the nineteenth century, “retorts” were commonly used with the pot stills making rum in Jamaica and elsewhere in the British Caribbean. These were usually paired, with the “low wines” retort receiving vapors from the wash still, rectifying them, and passing them on to the “high wines retort” for further purification before going to the condenser. With this setup, a full, high-proof distillation could be accomplished in one pass. Single retorts were also used for making some scotch malt whiskies. Retorts are still sometimes used in the Caribbean, but not in Scotland.
In North American practice, the column stills used for making straight whiskies are generally run “dirty”—that is, tapped in such a manner that the vapor coming off of them is less pure and lower proof than the machine is capable of producing—and doublers or “thumper kegs” (so called from the sound made by the vapor bubbling through the condensate) have traditionally been used to partially rectify that vapor. Many bourbon and rye distilleries still use them. They were also standard with the three-chamber still.
See also distillation, process; still, pot; and still, three-chamber.
Wiley, H. W. Foreign Trade Practices in the Manufacture and Exportation of Alcoholic Beverages and Canned Goods. Washington, DC: Government Printing Office, 1906.
Willkie, Herman F., and Joseph A. Prochaska. Fundamentals of Distillery Practice. Louisville, KY: Jos. E. Seagram & Sons, 1943.
Wray, Leonard. Practical Sugar Planter. London: Smith, Elder, 1848.
By: David Wondrich