London, June 3 : A new research by scientists will help to find the elusive chemicals that make a beer taste bad.
According to a report in Nature News, the taste of a beer that has gone stale or sickeningly sweet from being stored too long on the shelf, is quite bad.
For centuries, the chemicals behind these flavours have been a mystery, but new research is now revealing the elusive compounds.
As beers lose their freshness, they first take on bready flavours, which later shift to flavours known as cardboard, sweet, caramel, wine and sherry.
While some of those might sound delicious, when generated unintentionally, they can taste revolting.
Throughout history, efforts to keep beer fresh have centred on the concept of keeping it out of contact with air throughout the brewing process. Although that strategy keeps some unpleasant flavours at bay, beer still eventually goes bad over time.
This led Adriana Bravo and her colleagues at Polar Breweries and Simon Bolivar University in Caracas, Venezuela, to hunt for other causes of flavour deterioration.
The team first found that a chemical reaction called the Maillard reaction, in which sugars are broken down by reactions with amino acids, was taking place in beer sitting on the shelf.
"The Maillard reaction is one that is usually seen in baking and roasting where temperatures are high," said Bravo. "That it was taking place during beer storage where temperatures were 15-20 degree C was really surprising," she added.
Bravo and her colleagues suspected that intermediates of the Maillard reaction, called alpha-dicarbonyls, are involved in the change in flavour, because they had observed a chemical marker of the reaction increasing in beer as it aged and deteriorated.
They could not be certain, however, without putting a stop to the Maillard reaction, so for experimental purposes they added the drug aminoguanidine to the beer.
Aminoguanidine has been under clinical trials in diabetics to control the reaction of sugar with proteins and enzymes inside the body.
The team added it to beer to shut down the Maillard reaction without making the beer toxic. When they tasted the doctored beer, they found that even though it was old enough to have developed unpleasant flavours, none was present.
According to organic chemist Paul Hughes at Heriot-Watt University in Edinburgh, probing the Maillard reaction at room temperature and quantifying the intermediates involved could ultimately help prevent flavour deterioration.
"But whether these specific pathways are the ones that cause the most noticeable flavour changes remains to be seen. There are thousands of compounds in beer and we still have a lot to learn," he added.