COPENHAGEN (Reuters) - It is almost a barman’s dream - a keg that can monitor beer levels and alert the brewery for more supplies when stocks are running low, cutting the risk of running out of beer.

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Not only that, the keg can keep beer fresher for longer, banishing the scourge of the flat pint.

Pity it just can’t change itself yet.

Faced with stagnating sales of mainstream beer, and drinkers switching to wines and spirits, brewers have been forced to innovate to keep bar owners happy and sell them a broader range of products, helping them boost their own margins along the way.

Danish brewer Carlsberg is introducing the smart beer keg, allowing bar staff to monitor keg levels real-time on a tablet. The data it collects will help both the brewer and the outlets predict which beer will be in demand at certain times of day or during the year.

“This allows us to make sure the right product is available at the right place at the right time,” Nancy Cruickshank, who heads digital transformation at Carlsberg, said in an interview.

The smart kegs are made of plastic rather than the traditional heavy steel, commonplace for the last 60-70 years.

Carlsberg’s keg is being rolled out in Western Europe and some Chinese cities, while the digital system around the keg has been tested in Berlin and will be launched in Copenhagen, Malmo and Milan next month.

Carlsberg is not the only brewer with a PET plastic keg. AB InBev, the world’s largest brewer, offers Stella Artois and other brands in its “PureDraught” kegs, while global number two Heineken has a variety of beers for its “Blade” and “BrewLock” systems.

The new lighter plastic keg uses compressed air to push out the beer rather than CO2, which keeps it fresh for up to 30 days compared to less than a week with the old steel kegs.

Carlsberg says it allows bars and restaurants to try out some of the lesser known and more expensive beers because they don’t run the risk of the beer going flat.

This also helps brewers in their drive to boost margins, with sales of more premium brews, including craft, and gives drinkers the chance to sample them as draught rather than just in bottles.

“This very much fits with consumers’ demand for different types of tastes and products. And they’re really willing to pay for them,” Cruickshank said. “This is a chance for us to access a higher-margin market.”

The switch to plastic goes against an increasing trend among food and beverage makers to turn away from single-use plastic packaging, as consumers become more environment conscious. Carlsberg said although the kegs are single-use, it is working on a plan to collect and recycle them.