Whisky Magazine Issue 121
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We look at conditions within warehouses used to age bourbon
?The character of a bourbon is determined by the character of the spirit, the barrels used for ageing, the length of ageing, and conditions within the ageing warehouse. The key factor in ageing warehouses is the temperature profile, which instigates various reactions that facilitate the ageing process.
The temperature profile varies depending on the type of warehouse, with the options including brick, stone or metal clad warehouses.
"We only use metal clad warehouses, which transmit temperature more readily than any other type. We're looking for as much heat in summer, and as much cold in winter," says Rick Robinson, Plant Manager, Wild Turkey.
Location also matters. Warehouses on hill tops are more exposed and experience greater temperature extremes than warehouses in valleys, which are more sheltered.
Changes in temperature prompt a vital process known as a ‘cycle.' As the temperature rises in spring and summer the spirit expands within the cask and penetrates into the oak staves, which contain various flavour compounds. As the temperature cools, during the autumn and winter, the spirit contracts and exits the oak, carrying flavour compounds (which add vanilla notes, for example) back into the ‘bulk' of the spirit.
A related factor is the height of a warehouse, which can comprise seven floors or more. Additionally, each floor holds three tiers of barrels, sitting on rails, which means a warehouse with seven floors can store barrels 21 high. This scale also me...