Whisky Magazine Issue 94
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Ian Wisniewski asks what do the terms first fill and second fill mean in relation to aging malt whisky?
Malt whisky is aged in casks which can be used more than once.
A cask used for the first time is referred to as a first fill, which could for example mean a 12 year aging period, before the cask is emptied and filled with new make spirit for a second time, when it's referred to as a second fill. Casks may be filled a third or even fourth time. Each fill has a different influence on the flavour of the resulting malt whisky, which means the fill is a significant factor.
Casks have previously been used to age either bourbon or sherry, with each type of cask contributing a different range of flavours to the maturing malt whisky. Bourbon barrels add, for example, vanilla and a light sweetness, while sherry casks lend richer sweetness with a range of fruit cake and dried fruit notes.
Each time a cask is filled the influence of the oak on the maturing malt whisky is reduced.
Let's look at a first fill bourbon barrel used to age malt whisky for 12 years. When filled for a second time, and used for a further 12 years, the influence of this barrel is typically around 25 to 30 per cent compared to the first fill. The influence of a third fill, another 12 years, would be around 10 per cent of the first fill.
By comparison, the second fill of a sherry cask typically has an influence of around 50 per cent compared to the first fill, with a third fill around 15 to 20 per cent, and a fourth fill around 10 per cent. The influence of a sherry cask doesn't reduce as rapidly as a bourbon ba...