Years ago in a former job, Patrick Walsh, owner and manager of the Commercial Club Hotel in Fitzroy, was cleaning out the wine cellar and found a few cases of Coopers Sparkling that the restaurant said had been there too long. “I contacted the brewery, worked out with them from the serial numbers how old it was (about two years), asked them if it would be any good and they offered a resounding yes,” he says. “It is bottled conditioned, that is, secondary fermented in the bottle.”

This awareness about secondary fermented beers and their ability to age led Walsh to buy 10 kegs of Coopers Stout at the end of winter for the last three years and put them away until the beginning of the following winter for his customers. “When Coopers found some in the warehouse, they asked me if I wanted some of it and I took it all,” he says. “It's financially stupid, but the time in the cellar takes some of the bitterness out and rounds the flavour up deluxe.”

The same secondary fermentation that occurs in a 50-litre keg can also happen in a 375ml bottle. Known as bottle conditioning, the style of beer determines the need for a secondary ferment in the bottle or not. “We bottle condition five of our beers,” says Simon Fahey, technical manager of Coopers Brewery, based in South Australia. “The Mild Ale, Pale Ale, Sparkling, Vintage and our Stout.”

But not all of these brews will be able to handle the aging process. Fahey explains, “The beers that can age will have higher alcohol levels, I wouldn’t try to age the Mild (3.4% alc/vol) or Pale Ale (4.5%), but the Sparkling (5.8%), Vintage (7.5%) and Stout (6.3%) are high enough in alcohol to be stored.”

Just how long you can store these beers is another matter. “How long is a piece of string?” quips Fahey. “It depends on how the beer is stored. If it’s kept at a cool temperature in a dark place… years.” The longer a beer is left to age, the less carbonation it will hold and as a result the beer often mellows, bringing forward a more subtle flavour profile than when it was initially bottled.

Beer is usually conditioned in one of two ways: brewery conditioned or naturally conditioned. Brewery conditioning refers to the brew being fermented in large bulk tanks and filtered – think of lagers and pilsners, which are crisp, clean beers – where naturally conditioned beers aren’t filtered and carbonation takes place in the bottle through the addition of natural sugars and yeasts. A trained eye and expertise is needed to keep these brews in check. They may be a little pricier than your usual Carlton Draught, but skill and time costs money.

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Dave Bonighton, chief brewer at Mountain Goat Brewery in Richmond, partially bottle-conditions two of the brewery’s beers: the Steam Ale and High Tale Ale (both 4.5% alc/vol). This gives the brewer more control over the final outcome of the beer rather than leaving it all to what happens in the bottle. “We conventionally carbonate the beers in a tank to whatever we feel is right and then put the beer in bottles, add a little fermentable sugar and yeast, cap the bottle and the yeast moves through the sugars creating alcohol and carbon dioxide.”

The partial conditioning means that, while these beers may not age like beers with higher alcohol content, they are non-filtered in their second ferment which gives them a complexity of flavour – fruity, cloudy, full and delicious – on the palate. It takes one or two weeks to achieve the bottle ferment and Bonighton has learned how to control the ferment to achieve the beers he wants.

Buying beer to put away in a cellar the way we would wine isn’t something that’s often considered among those outside the brewing and selling community, but the fact we may be able seek out aged beers in pubs and bars creates more opportunity to taste and learn what happens to beer over time with proper storage.

Indeed, with the end of winter approaching, there’s a couple of weeks to get to the Commercial and try Walsh’s aged Coopers Stout or simply ask your local about bottle conditioned drops. It’s always a good excuse to try a different beer.