Whisky is made from a cereal; some (or all) of it malted, that has been ground into a rough flour then mashed by passing hot water through the flour to extract a sweet liquid. This is cooled, yeast is added and the mixture ferments, turning into a crude beer. This is then distilled in either a pot or a column still. Because alcohol boils at a lower temperature than water, the alcohol vapours are released. These are condensed into a clear, strong spirit which is then aged in oak casks.
Malt whisky is made exclusively from malted barley and is distilled twice (or occasionally three times) in pot stills. It is distilled in a column still to produce a lighter spirit with a high degree of alcohol and aged in used casks for a minimum of three years.
Irish whiskey can be made in a variety of styles. Pure pot still, using malted and/or unmalted barley; a mix of pot and column still, and all column still. It, too, must be aged in used casks for three years.
American whiskey (bourbon) must be made from a minimum 51 per cent corn, to which can be added wheat, malted barley and rye. It is distilled in either a single column still, a column still with a second still called a ‘doublet’ or in pot stills.
Canadian whisky is a blend of whiskies most commonly made in column stills from wheat, corn, barley and rye (either singly or combined), and must be aged for a minimum of three years in used oak casks. Canadian distillers are allowed to add up to 9.09 per cent of other mature spirits (Cognac, rum, bourbon, malt, sherry) to the final blend.