Scientists from the Complutense University of Madrid (CUM) developed a method that allows brewers to measure the freshness of beer using a polymer sensor that changes colour upon detecting furfural, a compound that gives aged beer a stale flavour.

The sensor can be controlled via a smartphone app also created by them. Beer is one of the most widely consumed alcoholic beverages in the world. The flavour of each brand is one of its most relevant quality standards.

However, depending on the beer type and its storage conditions, flavour may be altered as a result of changes in the chemical composition produced during beer with a negative effect on the quality of the flavour, researchers said. The new method is simple and low-cost and is capable of measuring whether or not beer has gone stale, simply by using a sensor and a smartphone app, they said.

Until now, brewers have measured furfural and other freshness indicators using methods based on chromatography techniques, researchers said.

"But these methods involve the use of expensive equipment and sample preparation is very time-consuming," said Elena Benito-Pena from CUM.

The system developed by researchers consists of sensor discs that detect the presence of furfural in beer.

These sensors, made from a polymer similar to the one used to manufacture contact lenses, have been designed to change colour (from yellow to pink) when they come into contact with a beer containing furfural.

"We have incorporated an aniline derivative into the sensor material which reacts with the furfural and produces a pink cyanine derivative that allows us to identify the presence of the marker in the sample," researchers said.

"The intensity of the colour increases as the concentration of furfural in the beer rises and, thus, as more time passes since the beer was produced," they said.

Researchers have also created a mobile app for Android smartphones that, by analysing a photo of the sensor disc, identifies the amount of furfural present in the beer. With this data, the degree of freshness can be determined. The study was published in the journal Analytical Chemistry.

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