Most gins and vodkas made in this country are made from grain spirit. This is made in whisky distilleries alongside the whisky itself - it's the same stuff. Normally at around 96% by volume. Then what's going to be whisky gets put into wooden barrels for a period of a minimum of three years. This is the time that the flavour gets into the spirit, from the barrels themselves.
The remainder gets run through the still again. Then it's known as 'rectified spirit' or 'neutral spirit'. This gets taken to gin and vodka distilleries. It may get distilled a third time, it certainly used to at Beefeater Gin when I worked there 25 years ago. And then flavouring is added to the gin. No flavouring to the vodka. Then it's reduced to the normal bottling strength of 40-odd percent by simply adding distilled water.
All potable alcohol is made by cooking vegetable matter with yeast and cleaning up the result. What you get depends on what you start with. Beer from hops and grain, cider from apples, wine from grapes, whisky from wheat or malted barley. Some vodkas are made from potatoes, tequila comes from a cactus and brandy is alcohol that has been distilled from wine.
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