Barrel Aging


Since we have had a nice big haul of some of the best Barrel Aged and Fermented beers arrive, we thought it’d be a fantastic time to take a closer look at the technique, and speak to some of the people continuing to pioneer in the field today.

The use of wood in brewing is definitely not a new innovation, with industrial brewing predating the development of stainless steel by several millennia. As an abundant natural resource that could be formed into watertight structures it was the dominant material for building breweries in the Northern Hemisphere for most of history. Amazingly, there are still some wooden brewing vessels in use today that are several centuries old, such as the russian oak fermentation vessels at Traquair House.

The history of barrel aging beer is intrinsically linked to the same process in the global whisky industry. Contrary to popular belief, Scotch whisky hasn’t always been aged in oak casks, this process is actually considered to be a much more recent development, starting around the beginning of the 19th century.

Bourbon barrels at Huyghe filled with Delirium Tremens

In an origin legend not unlike that of IPA, it is alleged that whisky was eventually required to be shipped further afield, and oak casks were the natural choice. The whisky coming out the other end of the voyage was generally tastier, and easier to drink, and the practice evolved from there. Unsurprisingly this same origin story is mirrored on the other side of the Atlantic with bourbon and the paddleboat journey the length of the Mississippi river taking several months.

The use of Wooden barrels for storage and transportation of just about every commodity that it’s possible to imagine plays another essential part of the story. These barrels may have arrived at distilleries after holding pretty pungent goods, fish, or pickles for example, they would be given a quick and intense blasting with fire on the inside to remove any lingering traces of the previous occupant. This charring had the unintended effect of making them excellent vessels for aging whisky in. The layer of charcoal produced acts as a natural filter for some of the unpleasant notes produced during fermentation and distillation. But most importantly, the charring causes the breakdown of the wood sugars, lignin and hemicellulose, that are essential for contributing that classic sweet vanilla and coconut flavour to the Whisk(e)y.

When it comes to beer, there are two approaches to consider; fermentation/maturation in wood, and the use of pre seasoned casks to infuse flavour. In the 18th century, beer was shipped immediately after primary fermentation, with further maturation or aging left up to the eventual landlord or consumer. A preference for longer aged beers quickly developed, particularly among Porter drinkers (at this time Porter was in fact one of the widest produced beer styles), this of course led to the aged beers fetching a higher price. Not wanting to lose out on this lucrative opportunity brewers began to take the maturation process back in house, and started to construct vast wooden vats to age the beer in. It’s alleged that Eugene Rodenbach, Grandson of the original owner of the Rodenbach brewery, spent time in England in the late 1800s studying the methods used by Porter brewers and now the famous Roselare brewery has an enormous cellar of 300 oak foeders for maturation. These porters would of course have tasted quite different to today’s, primarily due to the malt used being totally different, but also because the porous surface of the wood makes for a fantastic environment for yeasts and bacteria to set up camp. These microbes will work away throughout the maturation to turn any remaining sugar into acids and esters, potentially taking several years to do so.

This approach to barrel maturation is most evident in the Pajottenland of Belgium. The primary inoculation of lambic is done in the koelschip, before the wort is sent to ferment in barrels, where there are also resident populations of microbes too. The many different strains and species all work under different conditions, with varying tolerances for pH, temperature, and alcohol concentration, so will kick in at different points through the long drawn out fermentation process. Some of these, such as brettanomyces or acetobacter, will enjoy an environment with access to oxygen, which can be exchanged through the porous surface of the wood. Typically lambic brewers are not looking to express flavours from the barrel, or it’s previous occupant in their beers.

Spontaneous fermentation well underway in a barrel at Timmermans
Spontaneous fermentation well underway in a barrel at Timmermans

The more contemporary approach to beer barrel aging is to select casks specifically for the character they retain from the previous fill, to impart this flavour to finish the beer. The precise origin of this as a technique is shrouded in the mists of time, despite being a fairly modern development. Some suggest that Goose Island’s Bourbon County was the first, in 1992 (although this is heavily disputed and 1995 the more likely date), while others would argue that it was Samuel Adams Triple Bock released in 1994 to celebrate the brewery’s 1000th batch. Either way, both of these beers set a precedent that would soon become a template used across the world. Both beers were very strong, Bourbon County is 14.2%, and the Triple Bock 18%, with high finishing gravities, and both were aged in Bourbon barrels. The annual release proved extremely popular for Goose Island and almost twenty years later led to the opening of a mind bogglingly huge barrel aging facility, covering 13,000 square feet, housing thousands of barrels of various Goose Island beers.

A tiny section of the vast barrel store at Goose Island

It’s no surprise that these pioneers chose Bourbon barrels to age their beers in. Since 1964 it has been federal law that Bourbon must be aged in virgin oak casks, this was partially in response to pressure from Coopers’ unions to save their industry when demand tailed off after the Second World War. Given the enormous volume of Bourbon produced in the United States, and it only needing 3 years to mature, there is a wealth of ex-Bourbon casks available for rehoming. Most of these are snapped up by the Scotch whisky industry, but there’s still an abundance available for brewers too. Although these barrels have been used for a few years for aging bourbon, there’s still plenty for the oak to give.

Within the oak itself there are some compounds soluble in alcohol, and some soluble in water. Thus the bourbon primarily extracts the alcohol soluble flavour compounds, leaving plenty for the more water rich beer to access. The barrels will also have what’s colloquially known as ‘the Devil’s cut’ too. Contrary to the Angel’s share (the volume of whisky lost evaporating off into the air), this is the whisky that is absorbed by the porous wood. Not only does this directly add the flavour of the whisky to the beer, but it will also have the effect of giving a slight bump in ABV too, sometimes as much as 1-2%. This devil’s cut is of course not exclusive to whisky, and will be found in all other pre seasoned barrels.

Sara Laurienti, Director of Brewery Operations at Oskar Blues Brewery in Longmont, Colorado says that they barrel age beer ‘to create flavors and aromas that would be impossible without aging in oak. While we can replicate a lot of these flavors by adding oak spirals, we get a lot more by letting beer sit in barrels and allowing the wood to warm and cool with the seasons. Aging in barrels also allows us to play with other types of liquor without the need to add anything directly to our beer.’ They currently manage around 1000 barrels of aging beer, totalling about 1200 hectolitres, which they manage seasonally. At this point in the year they are between their emptying and filling season, having just emptied 580 bourbon barrels, 100 rum barrels, and 100 brandy barrels, leaving around 100 ex-Scotch whisky barrels holding an imperial sweet stout for around another 5 months.

‘When it comes to picking specific barrels a major thing I look at is how long they have been sitting empty. The fresher the barrel the better. Our bourbon barrels ship directly from the distillery and are emptied based on our order, so they are empty only 3-5 days before we refill them with beer. I also like to get in at least one type of barrel we have never used before. Last year we used unpeated Scotch barrels. This year we are getting some applejack brandy barrels from upstate New York I’m pretty excited for.’

Barrels being filled at Oskar Blues

Finishing beers in a barrel isn’t quite as easy as picking out a nice barrel freshly disgorged of a tasty spirit and slinging a stout in there though. While the porous nature of the barrels has a beneficial effect on flavour, it comes with the risks of bacterial infection and oxidation that need to be managed.

Sara at Oskar Blues finds that ‘the biggest challenge is keeping everything as sanitary as possible. Normally we only deal with beer in sanitized closed vessels, but for barrels we don’t have that option. Over the years we have gotten pretty good at creating an assembly line every time we fill so that we can open the barrels, purge with CO2, fill, and reseal the barrels as quickly as possible. Even with this process there is still always a risk. This is why we always do a quick sensory on every barrel before emptying to make sure we don’t blend in anything that isn’t up to our standard.’

Oxidation is normally considered an off flavour in beer. Typically associated with a wet cardboard or papery aroma making a beer seem stale and lifeless. When managed correctly the slow exchange of oxygen through the porous wood can bring flavours similar to those found in drinks like sherry and madeira, which over time will help maltier flavours come to the fore, one of the reasons that make big stouts and barley wines obvious candidates for barrel aging. This doesn’t mean that more oxygenation, or longer aging, automatically makes for a better or more flavoursome beer though. If left to run on too long the beer will start to stray into the vinegar territory and develop acetic notes, especially since acetic acid producing acetobacter enjoy the presence of oxygen.

These factors are particularly important when considering long term fermentation in wood, like in the production of lambic. Sara feels that this approach to wood is more challenging ‘when we are finishing beer in wood, we are only using the barrels for the last step of the process to enhance what we already created. When beer is fermented in barrels it can be a lot less predictable, and a lot messier, since the beer is still active.’

Gert Christiaens, Chairman of HORAL, and Owner-operator of Oud Beersel, agrees that fermentation in wood is more complex ‘when putting beer in a barrel for a long term you need to take more factors into account like oxidation, temperature changes, the microorganisms active in the beer, the brewing recipe, etc. Finishing a beer in a wooden barrel, previously used for strong alcoholic drinks before will limit risk of infection, and it’s mainly about extracting flavours from the barrel.’

Wood aging is absolutely essential to the production of lambic, and is one of the factors that make it such a truly special beer style as it’s not really possible to cut corners with. Lambic blenders choose their barrels on a different set of criteria, that is more focused on the structure and quality of the wood itself. Gert ideally looks for barrels with low tannins. ‘We purchase second hand barrels, and preferably from red wine. The condition of the barrels is important of course, as we want to use these barrels for decades. Barrels are mainly used for micro-oxygenation and for their secondary inoculation. The barrel should not give off-flavours to the beer, but normally the barrels are not selected to let the wood character to shine out.’

There is some scope for lambic brewers to experiment with barrel finishes though. Famously 3 Fonteinen have occasionally released their Zenne y Frontera, a blend finished in Oloroso and Pedro Ximenez casks. Gert himself has experimented previously too, releasing Oud Pipjen, a blend finished in Port pipes, the pipes themselves being between 60-120 years old. There’s also further barrel finish experimentation to come from Oud Beersel, Gerts hints that they have some Lambic on Whisky casks in their cellar. But most importantly they use these barrels only for finishing the components of a future blend. The lambic still goes into the regular barrels for fermentation.

In the wood cellar at Oud Beersel (as at some of the other lambic producers) there are barrels of many different sizes, alongside much larger foeders too. Before 2009 they only fermented in smaller barrels, until the addition of a set of foeders ranging in age from a few years up to over a century old. There is a distinct difference in the way these different sized vessels age the beer. Gert finds that ‘Lambic on the small barrels evolves faster and is more pronounced in flavor, lambic from the foeders evolves slower and the end beer is more refined.’ There are a number of factors at play here, but one of the most important is the surface area to volume ratio. Larger foeders will typically have a lower area of wood available to work on each litre of beer, it will also take much longer for oxygen to permeate through to the middle of the barrel so these notes will likely be less prevalent.

Gert working in the barrel cellar at Oud Beersel

While the use of wood for maturing beer is a centuries old practice, there is still some scope for innovation. Although oak is by far the dominant wood used there are brewers pushing this boundary too. Sara at Oskar Blues collaborated with Cigar City on their beer Bamburana, this was an Imperial stout aged in Whiskey and Brandy barrels, with the addition of dates and figs. But most interestingly the beer was then aged in a tank with spirals (these spirals provide a massive surface area to volume ratio from a smaller piece of wood) made from Amburana, a particularly aromatic wood from Brazil. Sara found ‘Amburana is a lot more flavorful and complex than traditional oak, it adds a lot of vanilla, ginger and cinnamon notes. I think there will always be room to innovate when it comes to barrel aging. From barrels made out of different types of wood, to different aging and blending techniques, there is a lot of room to innovate and grow.’

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