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Sure, the debate over IPAs versus light lagers might rage on, but there is one thing almost all beer drinkers can agree on: No one like old, stale beer. Now, researchers in Spain say they’ve developed a cheap and easy method to let brewers know when their beer might be past its prime.

Scientists at the Complutense University of Madrid have built sensors that not only change color when a beer goes bad, but when combined with a smartphone app, can tell you the brew’s exact level of freshness. The sensors work by measuring a beer’s levels of furfural – a compound that makes beer taste stale as it gets older. As more furfural is detected, the device changes from yellow to pink. Then, the app can analyze the color change to determine exactly how much furfural is in the beer.

Previously, breweries needed to use expensive high-tech equipment to get similar readings using chromatography techniques. The new sensors, which are far cheaper, have been “very satisfactory,” according to Elena Benito-Pena, co-author of the paper from Madrid. “The measurements have been taken using samples sent directly from the brewing company with different production dates and distinct degrees of aging. These same samples were also sent to a laboratory where they were analyzed using gas chromatography coupled with mass spectrometry. The results we obtained were completely comparable.”

Of course, for now, this new technology is intended specifically for breweries. But it’s not hard to imagine where a similar idea might be used to replace a “born on” date on a Budweiser. Or for Coors Light, maybe instead of the mountains turning blue when the beer gets cold, they changes color when the beer goes bad. Or the label on a Natty Light could just be permanently replaced by a pink-colored sensor