Recognising bourbon cask character
Most Scotch, Irish and Indian malt whisky spends time in barrels that once held bourbon. Those barrels give a recognisable set of flavours. Here is how to pick them out and why they show up so often.
Why so many whiskies use ex-bourbon barrels
US rules require bourbon to be matured in new charred oak containers. Once a barrel has held bourbon, it cannot be used for bourbon again. That creates a steady supply of good, used American oak barrels.
Scotch, Irish, Japanese and Indian distillers buy a large share of them. The large majority of Scotch spends at least part of its life in ex-bourbon barrels. So ex-bourbon character is the background flavour of much of the whisky world. Learning to spot it is like learning the taste of a base malt in beer: it is everywhere once you know it.
American oak gives vanilla and coconut
Ex-bourbon barrels are almost always American white oak (Quercus alba). That wood is rich in two kinds of flavour compound that matter here.
- Vanillin comes from the breakdown of lignin in the wood, especially when it has been toasted or charred. It gives vanilla, custard and cream.
- Oak lactones, often called whisky lactones, give coconut and a sweet, woody note. American oak is generally richer in these than European oak.
The char inside the barrel adds caramelised wood sugars, which read as toffee, caramel and honey. Char also acts as a filter, removing some harsh sulphur compounds from the spirit over time.
The full ex-bourbon flavour set
When you nose a whisky matured in ex-bourbon casks, look for:
- Vanilla, custard, cream.
- Coconut, sometimes sun cream or toasted coconut.
- Honey, toffee, butterscotch.
- Fresh fruit lifted by the wood: banana, pear, peach, citrus.
- Light spice: a touch of cinnamon or white pepper.
Colour is usually gold to pale amber, lighter than heavily sherried whisky. Ex-bourbon character tends to let the spirit show through, which is why distilleries known for a delicate spirit often favour these barrels. Our guide to recognising sherry cask character covers the contrast.
First fill and refill casks
The first time a whisky distiller fills an ex-bourbon barrel, it is called first fill. The wood still holds plenty of flavour and gives strong vanilla, coconut and toffee. The second fill gives less. By the third or fourth fill, the barrel is giving mainly gentle oxidation and a little colour.
So first fill ex-bourbon whisky is bold and sweet. Refill ex-bourbon whisky is quieter, more about the spirit itself: cereal, fruit and flowers with a light wood frame. Neither is better. A good blender uses both, often in the same bottle.
Many barrels are broken down and rebuilt as larger hogsheads of about 250 litres. A bourbon barrel holds about 200 litres. The larger hogshead has less wood surface per litre of spirit, so it works a little more slowly.
Indian heat speeds things up
In a hot Indian warehouse, spirit moves in and out of the wood faster than in Scotland. Evaporation losses are much higher too, well above the roughly 2% a year commonly quoted for Scotland. Our guide to the angel's share in Indian heat explains why.
For flavour, it means ex-bourbon character can build quickly. A young Indian malt from first fill ex-bourbon barrels can show a lot of vanilla, coconut and toffee for its age. That is not a fault. It does mean the age statement on an Indian whisky does not compare directly with the same number on a Scotch.
Telling bourbon cask from new oak
Bourbon itself is matured in new charred oak, which gives a heavier, sweeter, more intense version of the same flavours, plus more tannin and spice. A Scotch from ex-bourbon barrels gets the gentler second-hand version.
A simple exercise shows the difference. Nose a bourbon next to an ex-bourbon matured Scotch. The bourbon is all caramel, dark vanilla and charred wood. The Scotch shows lighter vanilla with more fruit and cereal from the spirit. The wood is the same species. The age of the barrel and the spirit inside are what change.
Where it gets hard
Spotting obvious first fill vanilla is easy. Telling a refill ex-bourbon cask from a refill sherry cask, or picking an ex-bourbon component inside a mixed vatting, is much harder. Those calls take practice against known samples, ideally with someone who can tell you when you are right.
In a warm room, let each glass rest a minute before nosing so the alcohol settles. Drink water alongside, keep pours small and never drink and drive.
Start with a first fill bottling
Your first step: find a whisky labelled first fill ex-bourbon and nose it beside a vanilla pod and a piece of desiccated coconut. Then nose a whisky that does not mention its casks. If the same notes appear at lower volume, you have probably found refill ex-bourbon. That is cask recognition, done with your own nose.
Common questions
What does ex-bourbon cask whisky taste like?
Typically vanilla, coconut, honey, toffee and fresh fruit, with a gold to pale amber colour.
Why do Scotch distilleries use bourbon barrels?
Bourbon must be matured in new charred oak, so used barrels are plentiful. Other whisky makers buy them and reuse them.
What is the difference between first fill and refill?
First fill is the first time a whisky distiller uses the cask, giving strong flavour. Refill casks give less wood flavour and let the spirit show more.
