In conversation with... Richard Kilcullen, head of sour beer production at BrewDog


BrewDog doesn't really do things by halves. From throwing taxidermy 'fat cats’ out of helicopters to driving tanks through the streets of London, founders James Watt and Martin Dickie have always had a soft spot for the theatrical. It’s no surprise, therefore, that the brewery’s dedicated sour beer facility is no exception.

The facility’s name, ‘Overworks’ is sprawled across the outside of the brew house in gigantic Hollywood style letters, while brightly coloured signs warn dramatically of the dangers of cross-contamination with the main BrewDog brewery. Entering the Overworks site even requires passing through a decontamination chamber’ fitted with antibacterial matting.


This may all sound a little overly dramatic, but given the wild and unpredictable nature of the bacteria and yeast present on site at Overworks, not to mention the potetial financial cost of ruining a 300hl batch of Punk IPA, it is a necessary precaution.

“It was really important for us to put some physical, real distance between this site and the main brewery,’ Dickie explains in the Overworks mezzanine taproom bar. “So what we are doing is brewing on our 100hl brewery across the road and then pumping that output underground over here for fermentation.” 


The man responsible for overseeing that fermentation, and turning the wort that arrives at Overworks into deliciously complex beers, is head of sour beer production at BrewDog, Richard Kilcullen. The former Wicked Weed brewer was persuaded by Watt and Dickie to leave North Carolina behind to head to rural Aberdeenshire, and so far he doesn’t have any regrets.

“The project and level of investment here by these two [Watt and Dickie] is unreal,” he says. “I worked for one of the largest sour producers in America and it took us five and a half years to get to this kind of level. The equipment and investment has meant that everything is top of the line and it is a really exciting project to be a part of. “ 


Entering the Overworks facility for the first time, it’s hard to disagree with Kilcullen’s assessment. The £4.5m project, which has taken over a year to complete, is of a scale that has never been seen before in the UK.

Ten 50hl and eight 100hl foudres tower imposingly above the brew house floor, while countless French oak barrels stretch back down the length of the facility. There’s also a 50hl coolship - reportedly a condition of Kilcullen’s hiring - in which the brewery will be producing spontaneously fermented beers in much the same way as the famous lambic producers of Belgium.


“We made the investment here with the aim of making the best facility of this kind anywhere on the planet,” Watt adds matter-of-factly. “I went to Wicked Weed about six months before they were bought out by AB InBev and visited their Funkatorium and I was blown away by the sour beers they were making there at the time.


“I managed to spend some time with Richard, and persuaded him to give up America and come to the north-east of Scotland and help us introduce people in the UK to these modern, American sour beer styles.”

Almost a year after arriving at BrewDog, the fruits of Kilcullen’s labour are finally ready to be released to the public. Among the first beers to come out of Overworks are Pyraster – a pear sour aged in red wine barrels and fermented with yeast from locally sourced blackberries, and Mariangela – a blended saison with blush orange and strawberries aged for two months in an amphora (a clay vessel similar to a barrel).


Those expecting lambic-esque acidity and sharp vinegar-like flavour profiles, however, may find themselves disappointed. BrewDog’s offering thus far so far is very much of the accessible, balanced variety, something Kilcullen says was a conscious decision when designing the recipes and monitoring the fermentation process.

“You'll notice that there is plenty of brett funk on the nose, but they are not overly aggressive in terms of the character,” he says. “We wanted to create really nice dry, balanced beer. I want these beers to be sessionable; I don't want everyone's teeth enamel to feel like they are coming off afterwards.


“The thing about sour beer that we have seen in the US is that is has been a bit of an evolution in terms of what the concept is. At first we had these really lactic, aggressive beers that mirrored our IPAs at the time; really intense, strong flavours. As palettes have changed we are now focussing on balance and subtlety.”

That’s not to say that these beers lack complexity or are of inferior quality. Indeed, BrewDog and Kilcullen were so keen to make sure that the first releases from Overworks were spot on, that in the first few months of operations around 30% of the faciliy’s output was going down the drain.

“I'm very unromantic about it,” he says. “We dumped a tonne of beer in the beginning. It's a slow process, and the stage we are at now the variability is nuts. From barrel to barrel the flavour profile can vary massively.”


Bolted onto the edge of the Overworks site, in a separate wood-paneled room, is Kilcullen’s pride and joy; a 50hl coolship in which the American brewer has been experimenting with spontaneous fermentation. Brewing to the specifications laid out by Frank Boon, Killcullen is seeking to emulate the likes of Brouwerij Boon and Cantillon, producing lambic-style beers fermented with wild yeast from the Ellon countryside.

“It’ll probably only be around one per cent of our overall output here at the site, but that’s not what it's about,” he says. “The process takes about 16 hours and two of your brewers so you are sacrificing a lot, but it’s something myself and James and Martin are so passionate about.”


So far, just three brews have taken place on the Overworks coolship, and its unlikely that the beers will see the light of day for at least a year. Nonetheless, Kilcullen is adamant he won’t be blending the spontaneously fermented product with inoculated sours from the main Overworks output to speed up the process.

“That's like putting ketchup on steak - absolutely not!” he exclaims. “I'm not going to go through all of the struggle and labour of making these beers and then blend it with stuff we are producing with the lab cultures. I'm very puritanical about how we treat these beers and what we do with them.”


Puritanical certainly seems like an accurate way of describing Kilcullen, and watching the curly haired brewmaster interact with staff in Overworks’ dedicated laboratory, it is clear that this is a man who likes to have control over every aspect of the brewing process.


“When you are working with wild yeast strains and starting from scratch it is basically just raw experimentation,” he admits. “However what we can control is the process. We are very clean over here. We apply all the same fundamental principles that all brewers learn and that is something I am very strict about.

“If you can keep the consistency of your process, then you can control the variability, and that is how you start to learn. Each beer is a little bit of a learning experience, but as you go on you are able to have more predictability in what you are doing.”

Of course, nothing is certain when it comes to sour beer, but with a brewer as meticulous as Kilcullen, and backers as ambitious as Watt and Dickie, it is hard to see BrewDog’s Overworks facility being anything other than a success.

This article originally appeared in issue 28 of Ferment magazine, and has been reproduced here with their permission.