Loaded barrels: An extract from Charles Maclean's essential guide, Whiskypedia
The cask in which whisky matures can determine over 80 per cent of the flavour. In this entry from his new book, Charles MacLean sorts the wood from the trees.
By law, Scotch whisky must be matured in oak casks. Most of the casks (around 90 per cent) are made from American white oak (Quercus alba), the rest from European oak (Quercus robur).
The species of oakwood influences colour, aroma and taste (together, the last two are the ‘flavour’ of the whisky). American oak imparts a golden hue and sweet, vanilla or coconut flavours; European oak, being more tannic, makes for a richer, umbrageous colour, a drier taste and typically introduces dried fruits, nuts and spices to the flavour, and sometimes sulphury notes.
The casks are invariably second-hand: they will have been used previously to mature bourbon (for around three years; always American oak) or will have contained sherry (for one to two years, usually Oloroso sherry; mainly European oak, some American oak). Occasionally ex-wine barrels, or wine-treated casks are used (mainly European oak).
Casks come in a range of sizes. The commonest are ‘barrels’ (about 200 litres, also called ‘American Standard Barrels’ or ASBs), ‘hogsheads’ (250 litres, also called ‘remade hogsheads’ – they are made by combining staves from ASBs; four of the latter make three hogs-heads), ‘butts’ (500 litres, usually made from European oak and ex-sherry) and ‘puncheons’ (also 500 litres, dumpier than butts; made from both European and American oak).
Casks are used three or four times before they are deemed to be ‘exhausted’. The first time they are filled with Scotch they are termed ‘first-fill casks’, thereafter they are ‘refill casks’. Once exhausted, they may be ‘rejuvenated’ by being scraped out and retoasted or charred.
● Extract taken from Charles MacLean’s Whiskypedia: A Gazeteer of Scotch Whisky by Charles MacLean, published by Birlinn Ltd, 2009. Reproduced with kind permission from Birlinn Ltd. www.birlinn.co.uk