There’s a pecking order among barrels. Mizunara casks sit at the top, unassailable on their lofty peak. After those come the pipes and puncheons that once held fortified wines: Pineau, Port and Pedro Ximenéz. Then there are the massed ranks of lowly ex-Bourbon casks, a staple of the barrel-ageing starter pack.
I rank them like this based on their rarity and the effects they can have on the spirits they contain. A barrel’s former contents can give a spirit a boost. So too can the type of wood from which it’s made. But that’s not the whole story. There’s also fire.
Barrel toasting and charring is increasingly influential in the ageing and finishing of spirits. American law says Bourbon barrels must be charred inside – literally set on fire for a minute or two. Why? Firstly, the layer of burnt wood acts as a filter, stripping away unwanted flavours from the spirit as it ages and mellowing any rough edges. As char takes it also gives, breaking down hemicellulose in the wood’s surface to form dissolvable sugars that create caramel, toffee, nutty and maple flavours. Lignin in the wood breaks down too and creates smoky, creamy notes as well as hints of vanilla, leather and spice. From tannins, the heat makes acids that can later combine with alcohol from the maturing spirit to form delicious esters. When it comes to ageing spirits, fire is most surely our friend.
As char takes it also gives, breaking down hemicellulose in the wood’s surface to form dissolvable sugars that create caramel, toffee, nutty and maple flavours
Some barrels are toasted rather than charred; heated without burning to alter the surface structure and composition of the wood. For spirits, this is most commonly found in STR (shaved, toasted and re-charred) casks. Distillers have been buying these up for a while and now that spirits aged or finished in these casks have made their way on to the market, the term is starting to appear on more and more labels.
Most distillers buy their STR casks from cooperages but for others a DIY approach is the only viable option. Alex James, founder and distiller at London to Lima, learned how to put barrels through the STR process during the COVID lockdowns in Peru, where the only casks he could get hold of were ex-wine barrels.
London to Lima has so far gained most press for its gin but James is using his STR casks to mature a rum, which he plans to release in the UK by the end of 2024. From buying his first cask in 2020, James has now expanded to 33. He starts each one the same way by shaving back the inside surface. ‘I take off up to three millimetres,’ he says. ‘Someone told me the sulphur levels reduce 13 times for every millimetre you shave, so maybe 3mm is a little excessive, but it does get me closer to fresher wood.’
Next comes the toasting. After some trial and error, the method he landed on was to stand his barrels on top of a mini oven set into the ground in which he lights a fire. ‘We do it with a local type of mesquite wood. I’m aiming for vanilla and spice balance,’ he says. It can take 90 minutes for the inside of the cask to reach its target of 200ºC, which James must then maintain for another 20 minutes — something he does with a combination of infra-red thermometer and gut instinct. Then all that’s left is a quick burn to refresh the layer of char.
There’s also a new kid on the barrel-burning block called dark aromatic toasting. This technique was developed by Brugal, a rum brand from the Dominican Republic. ‘We decided to experiment with dark aromatic toasting a few years ago,’ says Jassil Villanueva, Brugal’s fifth-generation Maestra Ronera. ‘It took approximately two years to perfect.’
Brugal distils its rum to 94.6% ABV on a stainless-steel column still. This leads to a light, elegant spirit and means most of the flavour you will taste in its rums develops after distillation by careful maturation in wooden casks. In the case of its new Maestro Reserva rum, these are ex-Bourbon casks followed by American oak Oloroso casks.
Brugal’s distillers do the dark aromatic toasting midway through the second maturation. They temporarily remove the rum from its casks, which they then toast while the casks are still wet. The heat (which rises to 360ºC over 45 minutes) draws ‘caramel pearls’ out of the wood. Once these have formed, the distillers put the rum back into its casks and the maturation continues.
Dark aromatic toasting marks an interesting departure and could be the start of further innovation in other spirit categories
Villanueva says the technique imparts a unique depth and complexity to the rum. ‘It enhances the natural sweetness and adds layers of rich, toasty notes, such as caramel, vanilla, and dark chocolate.’
This new technique, used for a rum, marks an interesting departure and could be the start of further innovation in other spirit categories as distillers begin to explore dark aromatic toasting for themselves. For now, though, if you want to taste what barrel toasting and charring can do, your best bet remains a whisky.
Five bottles that showcase barrel toast and char
Loch Lomond, Steam & Fire
Ten months finishing in heavily charred casks give this whisky a softly smoky edge over brown bread crust and orange aromas, plus perhaps a hint of pear. It’s velvety on the palate with oaky crême patissière, coconut, cocoa powder, cinnamon and black pepper.
£45, 46% abv, The Whisky Exchange
The Balvenie, 12 Year Old Sweet Toast of American Oak
Matured in American oak casks toasted over a fire fed with more of the same American white oak. You might expect a big thwack of flavour but this is delicate and complex: toasted grain aromas with marzipan, light honeysuckle, vanilla, coconut cream, orange and soft mint. Then a softly spicy kick, cloves in a cushioned velvet boot to see you on your way.
£56, 43% abv, The Whisky Exchange
Compass Box, Nectarosity
A new face joining the Compass Box core range in late July 2024, this is a blend of grain and malt whiskies aged in custom-toasted American oak casks. Juicy white peach and creamy mango melt into butterscotch, vanilla, soft cream, cloves and pepper. A most enjoyable dram to come back to again and again.
£52.25, 46% abv, The Whisky Exchange
Yorkshire Distillery, Filey Bay STR Finish Batch #4
Winner of an IWSC gold medal in 2024. Matured in ex-Bourbon and STR red wine casks. Porridge and rich brown sugar aromas with vanilla, orange and melon on top. On the palate, custard and oak leads into red berries with a lingeringly complex lemon-pepper finish. Seriously classy whisky from south of the border.
£60, 46% abv, The Whisky Exchange
Brugal Maestro Reserva
After four whiskies, here’s something different. This rum has complex aromas but sweetness is definitely in the ascendancy with bags of vanilla, honeysuckle, popcorn and caramel. On the palate (viscous, a little oily) you’ll find crême brulée, black pepper, fermented pineapple, dark toffee and guava. This is fun to drink.
£150, 41.2% abv, Master of Malt
