1. First, the rough wooden 'staves' – carefully measured planks of timber to you or me – are cut from the tree's trunk and left to season in the open air. The seasoning of the wood prepares the oak to contribute to the character of the whiskey.
2. The staves are ready for the barrel raiser. Barrels are raised, not built: no glue, no nails, nothing that might taint the whiskey – they're measured so they will fit together inside a metal ring and be watertight. The cooper (the name given to a barrel-maker) fits the staves together by hand using different widths and assembles the skeleton-like puzzle pieces, 33 staves per barrel. A seasoned cooper can raise 250 barrels in a single day.
3. Now it's time for toasting. The cooper gets the fire stoked and lets open flames pass through the raised staves in what will soon be the inside of the barrel. This heat releases many of the flavours locked inside the wood. These include the final product's distinctive vanilla accent.
4. The barrel is then ready for the roar of the char tunnel's flame. As it passes through the fire, more of the wood's natural sugars caramelise, providing the whiskey with an even greater depth of flavour.
5. Finally, a craftsman prepares the barrel for the metal heads to be attached and tightened. The hoops are put on the bunghole through which the whiskey will be poured. It's drilled and, under a cooper's watchful eye, the barrel is tested for leaks and faults.
6. At last, the barrel is ready to receive its whiskey. It goes in clear with a hint of flavour – a product known as 'white dog' or 'new make', and occasionally sold unaged – and will emerge years later, matured, with a rich, amber colour and a warm, robust taste.
Charred oak barrels are not only a vessel for bourbon while it ages – they're as much of an ingredient as the grains and the limestone-fed water. They give the liquid a lot of its flavour, especially the sweet vanilla and butterscotch notes, and all of its signature golden colour.
With a little help from the Brown-Forman Cooperage in Louisville, Kentucky – the oldest cooperage still making barrels today – we've got the inside track on how to make one. Browse the gallery above to see how.
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Click here to see what happened when we sent our associate editor on a tour of bourbon brand Woodford Reserve's distillery in Kentucky.
