Still

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For other uses, see Still (disambiguation).

A still is an apparatus used to distill liquid mixtures by heating to selectively boil and then cooling to condense the vapor.[1] A still uses the same concepts as a basic distillation apparatus, but on a much larger scale. Stills have been used to produce perfume and medicine, Water for Injection (WFI) for pharmaceutical use, generally to separate and purify different chemicals, and most famously, to produce distilled beverages containing ethyl alcohol.

Application[edit]

Main article: Distilled beverage
Swan necked copper stills in the Glenfiddich distillery
Old Ukrainian vodka still
Zambian artisanal Kachasu still and cooler

Since ethyl alcohol boils at a much lower temperature than water, simple distillation can easily separate highly concentrated alcohol from a mixture. Usually a still used for this purpose is made of copper, since it removes sulfur-based compounds from the alcohol that would make it unpleasant to drink. Modern stills are made of stainless steel with copper innards (piping, for example, will be lined with copper along with copper plate inlays along still walls). Using this combination of metals is much cheaper as it prevents erosion of the entire vessel and lowers copper levels in the waste product (which in large distilleries is processed to become animal feed). All copper stills will require repairs about every 8 years because of copper erosion from the compounds it is designed to remove; this erosion is therefore unavoidable. The alcohol industry was the first to use anything close to a modern distillation apparatus and led the way in developing what is now a large part of the chemical industry.

There is also an increasing usage of distillation of gin under glass and PTFE, and even at reduced pressures, to facilitate a fresher product. This is irrelevant to alcohol quality, because the process starts with triple distilled grain alcohol, and the distillation is used solely to harvest botanical flavors such as limonene and other terpene like compounds. The ethyl alcohol is relatively unchanged.

The simplest standard distillation apparatus is commonly known as a pot still, consisting of a single heated chamber and a vessel to collect purified alcohol. A pot still incorporates only one condensation, whereas other types of distillation equipment have multiple stages which result in higher purification of the more volatile component (alcohol). Pot still distillation gives an incomplete separation, but this can be desirable for the flavor of some distilled beverages.

If a purer distillate is desired, a reflux still is the most common solution. Reflux stills incorporate a fractionating column, commonly created by filling copper vessels with glass beads to maximize available surface area.[2] As alcohol boils, condenses, and reboils through the column, the effective number of distillations greatly increases. Vodka and gin and other neutral grain spirits are distilled by this method, then diluted to concentrations appropriate for human consumption.

Alcoholic products from home distilleries are common throughout the world, but are sometimes in violation of local statutes.[3] The product of illegal stills in the United States is commonly referred to as moonshine and in Ireland, poteen.

References[edit]

  1. ^ "DISTILLATION APPARATUS". Plymouth State University. Retrieved 22 March 2014. 
  2. ^ Kister, Henry Z. (1992). Distillation Design (1st Edition ed.). McGraw-Hill. ISBN 0-07-034909-6. 
  3. ^ "State Distilling Laws: Is it Legal to Make Moonshine in Your State?". Retrieved 22 March 2014. 

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