Single malt whisky is made by distilling a mix of malted barley, yeast and water in a copper pot still. This must take place at just one distillery to carry the word "single". After distillation the spirit is filled into oak casks, where it must rest for a minimum of 3 years. 30 year old single malt whisky is one of the spirit world's greatest treats, and offers all kinds of flavour. The characteristics can vary hugely depending on the region and production techniques used. One thing is for certain, though, 30 year old single malts are rare and rather prestigious.