Shelf life

Picture this: it’s a roasting hot day, you’ve just trudged home from work and you reach inside the welcoming cool of your fridge for a refreshing, cold IPA.
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Picture this: it’s a roasting hot day, you’ve just trudged home from work and you reach inside the welcoming cool of your fridge for a refreshing, cold IPA. You crack it open - and there’s no familiar “psst”. Give it a sniff, and there’s no recognisable hop aroma. Warily, you push on, and have a sip, instantly regretting it as the taste of wet cardboard fills your mouth. Stale beer is obviously a big disappointment, and something that brewers go to great lengths to prevent. Stability of beer is a big consideration in brewery processes and is also one of the reasons lager has come to dominate over the past 50 years: you can ship it thousands of miles over many months, abuse it and leave it in the hands of careless publicans and it will still generally taste the same. This cannot be said of all styles though, or of smaller breweries, who haven’t spent decades focusing on brewing for extended shelf life like the bigger ones have.

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Most of us would agree that the best beer is the freshest beer, drunk as close to the day of release as possible - and preferably on it. From the moment a beer is deemed finished, thousands of flavour compounds continue to interact with each other in an endless meet-and-greet, speed-dating their way through chemical reactions that cause flavours to change and haze to form. Bitterness decreases, though harshness and astringency increase. Sweet aromas develop, as does the catty smell of blackcurrant leaves called ‘ribes’. Caramel, burnt, toffee-like, wine, whiskey and leathery aromas all increase as well as that delightful taste of cardboard. Evidently some of these developments are quite welcome; on the other hand, a mouthful of damp loo roll and cat piss is not. A beer’s shelf life is the time it takes for these developments to become noticeable, and can be anything from a few weeks to a couple of years, depending on how the beer was brewed, its style, and how it is looked after post-packaging.

“Beer shelf life is a two part thing,” says Elliot Murphy, a brewer at Bath Ales who happens to have a PhD in Chemistry. “The first is physical stability, which is related to the gradual formation of protein-polyphenol complexes over time. These precipitate and cause haze. The second is flavour stability (or staling), which can be affected by microbiological infection and high dissolved oxygen content in the beer.” Haze is reduced in many ways, from using good quality malt, with low levels of haze-forming protein, to separation of trub at the whirlpool stage and using cold conditioning to force haze to precipitate so it can be filtered out before packaging.

One of the biggest issues is oxygen. It creates haze by fueling the reaction that couples up polyphenols and proteins, and it triggers the release of free radicals, which are just crazy about reacting with anything they can work with. When a free radical reacts with something, that compound is said to be “oxidised”. Oxidised versions of flavour compounds taste different - and often unpleasant - compared to before. Oxidised melanoidins can taste almondine or sherry-like as well as “catty”; oxidized polyphenols and isohumulones (hop acids) generally have astringent flavours. Papery and leathery flavours come from oxidised long-chain aldehydes.

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Brewers fight against oxygen on a daily basis, at several stages of brewing. According to Elliot, some of the most important methods are: purging all tanks with an inert gas before filling them with beer (especially bright or filtered beer); measuring the residual oxygen content in a purged vessel to verify effective purging; flushing pipework with de-aerated water when transferring beer (Elliot writes, “This requires a de-aeration column, which is expensive.”); and having a bottle/can filler that is designed to reduce oxygen pickup on filling. “For a can this means effective gas flushing and for a bottle it involves sucking all of the air out of the bottle and refilling with inert gas at least twice before filling (double pre-evacuation).”

With the use of commercial fillers, brewers can reduce the amount of air in the headspace of a bottle to just 0.1ml. By contrast, hand-operated devices leave 2ml, which is a pretty dangerous amount since only 1ml of air is sufficient to oxidize all of the reductones (a class of aldehydes or ketones) in a typical beer. “This is the main reason why small breweries struggle with shelf life. Excluding oxygen during packaging often requires various pieces of expensive equipment,” explains Elliot. “The other problem is if they send their beer elsewhere to be packaged but in poor containers with no facility for gas purging.”

Not all is lost for the low budget microbrewery in the battle against oxygen, however. There is a cheaper, easier way to fight, and that is to harness the natural powers of yeasts, who scavenge for oxygen to use in their growth stages. Adding yeast to the bottle or a cask does the trick, though it does risk infecting the beer with bacteria if the yeast is no good. Bacterial spoilage can reduce beer’s shelf life to a matter of days, causing haze, sediment, acidification, gross flavours and sickly ropiness.

Toby McKenzie, who founded Manchester-based Redwillow, explains how he keeps the brewery “meticulously clean” to combat microbiological infection: “We use ATP testing at every single point during the production process to make sure the machines are completely sterile. ATP stands for adenosine triphosphate and is produced during respiration by every single living organism. We do ATP swabs of all the vessels before we put beer in them, all the fill-heads of all the canning lines are swabbed and tested, and we randomly test empty cans before they’re filled to ensure there’s no contamination.” Pasteurisation is used by bigger breweries, but it poses a couple of problems for smaller breweries. “It’s the ultimate way of preserving shelf life, but it’s ridiculously expensive,” says Toby. “For example, Robinson’s have got a million pound pasteurisation plant. Flash pasteurisation is very good for preserving beer, but if you’ve ever drunk pasteurised milk versus fresh milk, you know it has an impact on flavour.”

Distribution of the finished product is a whole other science, and careful co-ordination with pubs and suppliers ensure that no beer is wasted to staling by delivering just the amount that’s required. Sometimes breweries will manufacture their supermarket beers differently to ones destined for a bar. Toby explains, “Supermarket beers we tend to filter quite heavily, because we know it’s going to be on the shelves for six months at 24°C to 25°C.” As temperature increases, the rate of reactions does too, so by keeping beer cool (just above freezing to around 7°C) you can slow staling processes. Rob Brown, operations manager at Beer52, comments, “If we’re collecting styles that are heavily hopped like NEIPA’s, a style well-known for fading fast, or even IPA’s from Europe and beyond where the transit time is more than a day, we’ll have them transported in refrigerated containers or trucks to ensure they’re in the best possible condition on arrival.”

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Rob says Beer52 has a huge advantage over pubs and bottle shops when it comes to supplying fresh beer to the consumer: “The volume we require from each brewery is fairly significant. Small breweries simply don’t hold those kind of volumes, so the order can’t be made up of pre-existing stock. This means it’s produced fresh to order. There’s no sitting around on supermarket or warehouse shelves for months at a time before it’s in the consumer’s hand.” Beer52’s other advantage is the quick turnaround of stock due to the changing theme every month. “Generally we’ll schedule beers to arrive one to two weeks before production is due to start; in a matter of days the cases are being shipped out to our members.”

 Best before dates guide the customer and retailer about beer shelf life. Breweries usually determine this using sensory analysis - basically, tasting it themselves. “Any canning run, we keep back between twelve and twenty cans,” explains Toby at Redwillow. “We’re continually tasting those against fresh batches coming off and checking to make sure they’re pH stable, what the dissolved oxygen levels are over time, is the colour changing at all, is the aroma changing, is the taste changing.” Live cask ale will last a matter of days and kegged beer several weeks. Packaged, pasteurised beer that’s been refrigerated and kept out of direct light fares a lot better and can keep for up to six months, though after 90 days the flavour may start to degrade. IPAs may see a drop-off in hop aroma in about three months, but a Scotch ale or an import lager should be fine at six months. Delicate, hop forward beers have the shortest shelf lives, while higher alcohol or barrel-aged beers are given best before dates two years in the future. Stouts, porters, barley wines, Belgian Ales, and German Bocks have the longest shelf lives.

The best before date is not a number to fear once it has expired. Beers do not become dangerous or unhealthy to drink, only somewhat less palatable, or perhaps just too dissimilar to what the brewer was going for. But since they become unsaleable when expired, past-date beers have a different fate to their fresher siblings. Retailers may allow staff to take home any expired stock, or distribute it through charitable avenues. “We partner with a charity and donate any expired beers to them,” says Rob. “They recycle the glass and aluminium, sell it and turn that into cash. It’s a great solution on many fronts.”

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