A TEST normally used to detect heavy metal pollution in water could soon be helping ensure the beer you buy is always fresh. By measuring concentrations of the chemicals responsible for the 鈥渃ardboard鈥� taste of stale beer, it will help to predict which batches are likely to go off before their time. So breweries will be able to ditch batches that could have a short shelf life.
As any home brewer knows, making beer can be a tricky process. Fermentation involves nurturing a warm reaction in which live yeast feasts on a malt liquor. But even under controlled conditions, the resulting brew can vary widely in taste. 鈥淢aking beer is not like making a car, you don鈥檛 always get the same product,鈥� says Aquiles Barros, an analytical chemist at the University of Porto in Portugal. Minute differences in the beer鈥檚 composition can create a beer that lasts 5 months rather than 9 鈥� a huge problem for brewers and drinkers alike.
Today, breweries use human tasters to pick up hints of the 鈥渇lavour notes鈥� responsible for a beer鈥檚 potential to spoil. For example, a chemical called (E)-2-nonenal causes the telltale cardboard taste of stale lager. But while beer tasters have hypersensitive palates, their views are subjective and variable.
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Until now, tests sensitive enough to provide a more objective measure of the minute concentrations of the telltale chemicals have been too laborious and expensive. So Barros and his team developed an indirect test known as voltammetric analysis which is based on a technique used to find trace amounts of heavy metals in polluted water.
In their test, two electrodes dip into a simple vessel holding a concentrated distillate of the beer. By recording the way the current passing between the electrodes varies in response to a changing voltage, they can measure the concentration of two key chemicals, acetaldehyde 鈥� an indicator of the presence of (E)-2-nonenal 鈥� and sulphur dioxide. Because both molecules accept electrons at a known rate, the pattern of the current gives a measure of the concentration of the substances.
The team鈥檚 measurements closely matched the flavour ratings of human tasters 鈥� and even appear able to detect a broader range of concentrations than human taste buds. But further tests against larger groups of tasters are needed to confirm this.
Barros hopes the technique will provide a cheaper and more reliable way of assessing a beer鈥檚 flavour stability: 鈥淚n 20 years, tasting may even be replaced by chemical analysis,鈥� he predicts.
But Bill Simpson, technical director at brewing technologist FlavorActiv in Chinnor, UK, doesn鈥檛 believe beer tasters have anything to worry about. People can still detect certain compounds at super-low concentrations, he says, and the flavour of beer can be as complex as a glass of fine wine. 鈥淎 typical beer has 500 taste and aroma compounds,鈥� Simpson says, noting that the new test looks at only two.
