Walk into just about any craft brewery in Australia today and you will likely spot a few oak barrels hiding away in a corner somewhere.
Maturing beer in oak that has previously held spirit or wine is undoubtedly the hottest trend in flavour-led brewing, after the well-documented rise of highly hopped India Pale Ales.
At their best, these barrel-aged beers can be exquisitely complex. Take the Ramjet Whisky-Aged Imperial Stout from Melbourne's Boatrocker Brewing Company.
It has been matured in barrels that have previously held single malt whisky distilled by fellow Melburnians, Starward.
Prior to that, the barrels held Pedro Ximenez Sherry. In Ramjet, Boatrocker has seamlessly integrated both the first fill sherry and second fill whisky characters with the chocolate and coffee notes of the stout.
A fine balance
It's easy to 'over-egg the pudding' with oak maturation, seasoning a beer so heavily with spirit and wood as to render it undrinkable.
Boatrocker's careful technique was recognised earlier this year at the Independent Beer Awards of Australia (AKA The Indies), when Ramjet was crowned Champion Strong Beer.
Founder Matt Houghton says Ramjet's shared barrel ancestry with Starward Whisky is abundantly clear when you taste both side by side.
"There's a real similarity with the background flavour. I definitely get a red wine note in the whisky and it's fascinating that that translates into the beer as well," he says.
"This year's batch has been in bottle for a couple of months now. The whisky note is more prominent but as it ages it definitely becomes more integrated and you'll start seeing more of the background characters of the wood shining through a bit more."
High quality quota
Ramjet is dangerously drinkable at its 13.8 per cent ABV, which Houghton says has it well equipped for extended cellar maturation.
"The higher the alcohol content, the more chance you've got of getting easily five to ten years out of it," he says.
"We've got bottles of the 2013 Ramjet that are still drinking beautifully."
The whisky barrel imperial stout is the most common variety of barrel-aged beer, but some brewers are experimenting with ageing other beer styles in all kinds of weird and wonderful oak.
Hawkers Beer has recently released a series of beers in collaboration with Oregon, USA brewer Crux that have previously held Aquavit, the Scandinavian spirit distilled from grain or potatoes and flavoured with a variety of herbs.
"I have a very strong link to Scandinavia because my ex-business partner and best friend is Danish, so I wanted to do something a bit Scandinavian," says Hawkers' Mazen Hajjar.
The barrels were sourced from Norway's Linie, which rests its Aquavit in Spanish Oloroso sherry casks for further development.
When beer gets fun
Hawkers brewed a wheat wine – a high alcohol wheat beer – and seasoned it with the Aquavit barrels, adding notes of caraway, star anise, vanilla and sherry.
"It's medicinal in kind of a good way, like a schnapps but not a fruity schnapps," says Hajjar.
He says Hawkers now has about 140 barrels of beer maturing at its brewery in Reservoir, Melbourne.
"This is where we get to have fun – we get to go a bit crazy," he says. "We're trying to push public perception of what beer can be."
Take a look at the gallery above for some of the best aged beers to buy now.