The production of pure alcohol by distillation is not particularly difficult in principle — you simply have to make a batch of beer and then purify it. One cannot use a pot still however, or a moonshine still, or any of the strange little stills being written about and offered for sale on the Internet. This is because they do not incorporate the two essential requirements for high-purity fractional distillation. These two requirements are a) a packed column, and b) a split-stream stillhead.
In the earlier chapter where we discussed alcoholic beverages it was mentioned that simple distillation, using a pot still, divides the crude alcohol solution (or "beer") into three fractions — the heads, the tails and the middle fraction. The heads are the very volatile constituents of the beer such as acetone and methanol, the tails are the least volatile components such as fusel oils, while the middle fraction consists of mostly ethanol contaminated with both heads and tails. In other words the separation is far from perfect.
Theoretically, it would be possible to take this middle fraction and redistil it, thereby getting rid of a few more heads and tails. Then this process of re-distilling the middle fraction would be repeated over and over again until all the heads and tails were gone and we were left with nothing but ethanol. In practice, however, this is virtually impossible because we would be dealing with smaller and smaller volumes of middle fraction at each stage of purification until a negligible amount of ethanol remained. What good is one drop of pure alcohol!
Commercial producers of vodka, and other forms of pure alcohol such as that used in colognes, cope with this problem by adopting on a large scale the scientific process of fractional distillation. They use a counter-current flow of vapour up a tower (perhaps 100 ft high and 12 feet in diameter) against condensed liquid flowing down, the two meeting in a series of trays at many different levels within the tower. In these trays the rising vapour bubbles through the liquid and there is an exchange between liquid and vapour. For small-scale operations such as ours we use a packed column about 3 ft high and IV4" in diameter which serves exactly the same purpose as the commercial distilling towers. The construction of such a still will be discussed in detail later in this chapter.
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