We distil spirit that is clear. When it is filled into the cask the spirit looks like water – uisge beatha – water of life. It is during its time in maturation inside the cask that spirit develops its colour. Spirit develops colour from 3 things – the actual wood itself, the char of the wood and the liquid that was held in the cask before whisky spirit.
Before we fill with clear whisky spirit, we empty out all the sherry or port or wine that was held in the cask previously, But, some of the original liquid that has seeped into the wood of the cask can seep back out into the clear whisky and colour it – as well as flavour it. Most spirit nowadays is filled into a bourbon cask first. If we are filling into casks which have held bourbon and nothing else, we call this 1st fill. If the cask has held bourbon, then whisky, and now we are filling the cask with whisky for a second time, it is called 2nd fill. It doesn’t matter if it is your distillery or someone else’s distillery that has used the cask before, if this is the second time for Scotch in the cask, it is referred to as 2nd fill.
A rule of thumb is .. if your whisky is yellow gold or white gold it is likely to have only been in a bourbon cask. Think of all the colours associated with bourbon – yellow, gold, honey etc. If your whisky is reddish gold, amber or with red tints it is likely to have spent some time in a sherry cask – or red wine, or port cask. Of course these are easy generalisations to help you have an idea… they don’t always hold true. We can also get white/clear sherries and ports..how do they influence whisky spirit colouration…just to confuse the issue… ! Slainte!
Photo is sherry butts & bourbon casks in Ardbeg Filling store.