THOUGHT PIECE the carling team

Bring On The Barrels… Part 3


The stainless steel end of BrewDog’s Overworks with horizontal fermenters and conical conditioning vessels

BrewDog in Scotland is one place where the workings of Brett with a light souring from lacto and pedio is trying to be better understood. Brewmaster Richard Kilcullen from the USA has his own £4m Overworks where he says that wood, fruit and bugs work in harmony. It is on the edge of the main brewery site with strict microbiological control between the two.

OverWorks does not seek woody and whiskey flavours as in a barrel aged beer but uses the properties of oak to harbour microorganisms and allow a steady exchange of gases. Cultures of Lactobacillus and Pediococcus are held in a solera type system where younger beers which have produced agreeable flavours are blended back into the old and thereby pass on favourable characteristics. This inoculum is added to the secondary conditioning tanks using dedicated pumps and hoses to avoid ending up with the acid producers where you do not want them to be! Organisms can be obtained from yeast banks and the like but much work has been done from local hedgerows and fields to see whether Aberdeenshire harbours yeast and bacteria able to impart their own degree of funk. This lab work is key to trying to understand how the souring organisms interact with each other so that their optimum pitching rate, temperature and reaction time is known leading to more consistent finished beer flavour profiles.

The wooden end of BrewDog’s Overworks with over 1200 casks and eight 100hL wooden foeders (large casks) and another ten 50hL made in Italy by Romualdi

The first fermentation takes place in horizontal 120hL tanks complete with racking arms which can be rotated to ensure the top and bottom crops remain behind in the vessel after a four-day fermentation. This peaks at 33oC using a blend of Brettanomyces and wild Saccharomyces which attenuates to about 85-90%. Green beer is then transferred to 150hL conicals for a two week secondary fermentation period usually in the presence of macerated fruit (as well as herbs, spices and even honey). During the secondary fermentation, the mixed culture of Pediococcus and Lactobacillus is added if sour beer is to be made. Typically the temperature is in the high 20s.

After fruiting, the beer passes to a tertiary stage in wooden cask or larger foeder. The building contains over 1200 casks mainly of French and Hungarian oak which have already been home to red wine which tends to strip unwanted tannin flavours. There are eight 100hL wooden foeders (large casks) and another ten 50hL. Usually the foeders are used for sour beers as they tend to allow the development of acidity in a much more tempered manner due to the lower relative surface area to wood contact and thicker staves which result in a reduced induction of O2 during the slow barrel maturation. Thus there is less activity from aerobic bacteria such as Acetobacter which can sour a promising beer past the point of no return, but just enough oxygen for a long, slow Brettanomyces fermentation. Average barrel maturation time for a sour beer is 6-8 months and a Brett only is around 2 months.

Again many metabolic pathways are overlapping, symbiotically building upon one another in a delicate but hopefully predictable pattern. This interplay of organisms allows mixed culture beer to continue developing for months or even years. Varying times spent in contact with wood or different organisms result in vastly different flavours.

Overworks 50hL coolship waiting for a cool Aberdeenshire night.

Kilcullen also has a 50hL coolship with the end 10hL partitioned off for smaller batches of spontaneously fermented products. The walls are untreated white pine which are sprayed with inoculating beers. After natural cooling for 12 hours, the wort goes straight to wooden casks. He is also playing around with 10hL earthenware amphorae to see whether oxygen uptake can be controlled although unfortunately the green beer does tend to leach iron from the walls.

Old wort cooling trays at Elgood’s, now adapted for spontaneous fermentation with timber in the rafters.

Meanwhile, Elgood at Wisbech in Cambridgeshire has produced a series of lambic style beers originally called Cambic. Two 45hL coolships were made redundant in 1994 but removing them would have left a big hole in the floor beside the hop back. Brewer Alan Pateman was enthused by lambic techniques and has sawn up a fallen oak tree from the brewery botanical gardens and put it in the rafters above the coolships and hops are aged beside the boilers. The first brew after cooling went into stainless vessels with 146g/hL of wood chips and a touch of brewery yeast. pH came down to 3.11 and some was then put in barrels at a PG of 11.4. Brew two got some Brettanomyces added and the PG came down to 1005. The brews were blended and some fruit was added. There are now three beers, a straight 6%ABV lambic simply called Coolship and Coolship Fruit in raspberry/blackberry and mango infused versions at 5%. The biggest problem he said was having to disregard everything he had ever learned about keeping wild yeast and bacteria out of his processes!

Elgoods also supplies cooled coolship wort in 1000L transitanks to the Crossover Blendery which is on a farm near Stevenage. Crossover do the spontaneous fermenting bit in wooden casks at their site. They are producing some really interesting bottle conditioned beers with fruits, at some premium prices!

Operations at Crossover Blendery; a Coquard press to make juice and pomace, filling casks, adding a bit of cider to see what happens and the finished product on the right.

In 2017 Burning Sky was the first craft brewery in the UK to install oak foudres for aging beers, it has got its own coolship and has layered staves from wine barrels in the rafters above so that steam from the hot wort condenses and drips back into the wort carrying microbes with it. Many other UK micros are now experimenting. Harbour in Cornwall, strangely named as it is 12 miles inland at Bodmin has its Hinterland project now complete with a coolship has a 6.1%ABV Cherry Sour and has even had success using amphorae and sells a 750mL bottle at 7.2%ABV called simply Amphora for £13.99. Wild Beer in Somerset started off with three casks back in 2012 and now have 600 saying that it is the most creative of the new sour start ups. It sources yeasts from apple orchards and goes foraging for local botanicals and has 11 sours in its portfolio.

From the top left clockwise: The coolship at Burning Sky and products from Harbour Hinterland, Wild Beer, Crossover Blendery and Siren.

Few can be more prolific than Siren in Surrey which is famous for its Yu Lu tea infused beer (Earl Grey and lemon zest) and brought over 110 beers to market in 2021 alone; its Maiden and Odyssey ranges display excellent beers which have seen the inside of a wooden cask. Even established brewers like Stewart in Edinburgh and Derbyshire’s Thornbridge are in on the act; the former with a kettle soured Hedgerow Sour with mixed berries and Sour Sitron fermented with a kveik yeast while Thornbridge has a pair of barrel aged 7%ers with cherries and raspberries. You can keep up to date with Matthew Curtis, a beer writer from Manchester, who has his Pellicle Podcast series which tracks what he calls Modern British Beer.

It might be worth recapping on the souring techniques we have found. Most controllable is pitching a lactic acid bacteria preparation obtained from a yeast supplier. L delbruckii is often favoured as it is very susceptible to hop iso acids so if it does escape into the main fermenting room it is less likely to spoil mainstream beers. Pediococcus damnosus is slower acting, tends to produce a lot of diacetyl and is more resistant to iso acids. For new starters, the Wyeast 3278 mixture of yeast and bacteria will do the job.

The Germans have been using lactic acid plants for centuries as the Reinheitsgebot rules preclude the use of any chemical additions to the mash to adjust the pH of wort at pitching. The wort must be sterile, free of any inhibiting hop compounds and oxygen kept out by bubbling CO2 through. At up to 48oC, the process will take two days before the temperature is reduced and the bacteria laden brew is used. The residue can then be topped up to make another batch.

Taking the coolship to different environments. London Beer Co from Bermondsey and Noble Beast Brewing in Cleveland, Ohio.

Less predictable is mash souring where the mash is cooled to 40oC and a handful of milled malt mixed in, then left for two days. Kettle souring is similar but the malt is added to wort at 40oC for two days. It is best to boil the wort first without hops so that wort bacteria do not contribute. Or else you could transfer unhopped wort to a special tank via a heat exchanger which will allow the temperature to be controlled and avoid tying up one of the main parts of your brewkit for a couple of days. The wort is then boiled with hops to destroy the bacteria thus confining the bacterial process away from fermenting areas where there is a considerable risk of contamination. To do the souring faster, some brewers have read their sake making textbooks and have experimented with replacing 20% of the grist with white koji which is rice inoculated with Aspergillus oryzae. This produces a mix of citric, succinic as well as lactic acid. Users boast acidification in the time it takes to do a single mash. Other brewers will heave in a couple of pots of live yoghourt and leave it for the weekend!

Acidulated malt which has been inoculated with lactic acid bacteria at the maltings is another possibility provided the mash regime is adapted to allow the bacteria time to work. Some brewers will mash the acidulated malt separately at 72oC and mix the worts later. A pH meter is obligatory to track the acidity to the required level.

More barrels, this time at Lost and Grounded in Bristol and the finished premium priced product from Crossover Blendery

Souring in fermenter is another route. Brewers usually add the yeast first, allow it to attenuate by around two thirds before adding an actively fermenting acid addition. Otherwise the dormant bacteria can be added at pitch with their lag phase over by two thirds gravity. In the States you will see kombucha ‘beer’ where the fermenting agent is a SCOBY (symbiotic colony of bacteria and yeast) but the substrate is tea rather than wort and most are souped up with fruity additions. Brewers should beware that the kombucha process needs oxygen and produces a lot of acetic acid but that does not stop US brewers from having a go.

If all the above fails you will have to buy a coolship, install an old tree above it, leave the windows open and get a lot of wooden casks!

Just a final caution, if you are making trad beers and sour ones on the same premises even in separate buildings you must keep the processes entirely separate and that means people as well as equipment.

There is much enthusiasm with Brett and LB readily available, many will have wooden casks tucked away quietly composting. Let’s hope the market is ready for some complex and intriguing flavours. “The demand is there, people are ready for them” concluded Richard Kilcullen, BrewDog’s Funkmeister.