Whisky casks are living, breathing, things. They have to hold their whisky for years, sometimes decades. And, given a large enough parcel of casks held over a long enough time, chances are there may be the odd leak. While this is something to watch out for carefully, if managed well it need not be a major issue.
What causes a whisky cask to leak?
Whisky casks are hand-made out of a natural product, wood, and so they can sometimes leak. Potential causes of cask leaks include:
- Cracks, knots, and imperfections in the wood
- Loose or damaged staves
- Human error at the cooperage, or a faulty bung
- Bumps and knocks as the cask is moved, either between warehouses or around a warehouse
- Changes in temperature, which cause the wood to expand and contract
- Changes in air pressure, which again may cause the wood to expand or contract
- Wear and tear as the wood ages
Keeping an eye out for cask leaks
A good warehouse keeper will be constantly managing the whisky casks under their care. Signs of a leaking cask include damp spots on the outside of the cask that can be seen or felt, signs (or sounds) of dripping, and pooling of whisky below a cask. More scientific ways of monitoring a cask are checking its weight and ABV strength. If a cask has lost more weight than one may expect from evaporation alone, this could indicate a link. Equally, if a cask is low in volume but still high in ABV, this may indicate a leak has been the cause of loss of liquid - rather than angles' share.
By keeping a close eye out for such signs, action can be taken to repair the cask before any more whisky is lost.
What happens to the whisky?
Clearly, the worry is that the whisky will be lost. Hopefully, a leak is caught early on, allowing for repairs. In this case, the damage can be limited.
The whisky that remains in the cask may well be unaffected. Depending on the degree of damage to the cask, one factor that is worth checking for is oxidisation. As more air enters and circulates in the cask, more of the whisky will oxidise, changing the flavour. This is not necessarily a bad thing, it may result in a unique flavour profile. But, if you've had a moderate to severe leak, sampling the whisky may be wise.
Fixing a leaking whisky cask
If a cask has a minor to moderate leak, a skilled cooper has a range of potential ways to fix the issue. These include:
- Tightening the barrel hoops: using a mallet, the cooper can gently tap down the hoops, making the barrel staves tighter, and sealing up any small leaks.
- Using barrel sealant or wax: dry wax or melted wax can be rubbed into the leaking area or dripped onto the area to seal leaks.
- DIY paste: a mixture of 1:4 distilled water and unbleached flour can create a dough or paste-like combination which can then be applied to the leaking area. It is then dried using heat, sealing the leak.
- Using reeds, straws, or toothpicks. For small leaking spots, reeds, straws, or toothpicks can be gently pushed into the holes to plug them. This has to be done carefully, as you don't want to force a crack wider, making the leak worse.
Re-racking into a new whisky cask
If the leak is too severe to fix, the warehouse keeper may advise re-racking into a new whisky cask. This essentially means that the remaining whisky would be emptied from the old leaking cask and poured into a new, fully-sealed, cask. It can then continue its maturation.
This opportunity can be used to turn a nuisance into a positive, as while you could choose to re-rack into a similar cask to the previous, you could equally use it as an opportunity to re-rack into a different style of cask. For example, a sherry or port cask could be used to bring new and different flavours to the whisky.
Cask management with Spiritfilled
Spiritfilled is a full-service whisky cask broker. We help our clients buy, manage, and sell whisky casks. If we can help you with any whisky cask matter, we'd be pleased to help. You can contact our experts here.