The discovery came to light as a result of British researchers trying out a new and more accurate method of testing coffee quality.
Members of the team and collaborators around the world bought samples of coffee at shops and supermarkets. They found that a tenth of high-quality products labelled “100 per cent Arabica” contained significant levels of inferior and cheaper “Robusta” beans.
Arabica coffee trades at twice the price of Robusta because of its superior taste.
Adulteration with Robusta coffee, which is higher yielding and easier to grow, has always been a potential problem. But finding rogue Robusta in a sample labelled Arabica is not easy, especially after grinding and roasting.
The standard technique detects the fingerprint chemical 16-OMC, which is only found in Robusta coffee, but is costly and takes three days. This makes large scale surveillance impractical.
The new method takes only 30 minutes and is sensitive enough to detect just 1 per cent Robusta in a blended coffee.
Lead scientist Dr Kate Kemsley, from the Quadram Institute, formerly known as the Institute of Food Research, said: “This is an important milestone for detecting fraud in coffee, as 1 per cent is the generally accepted cut-off between trace contamination, which might be accidental, and more deliberate adulteration for economic gain.”
For the study a total of 60 different coffee samples were purchased in consumer countries around the world, including 22 from the UK.
All were tested for 16-OMC using the new nuclear magnetic resonance (NMR) technique, which employs radio waves and strong magnetic fields to obtain detailed information about a substance’s molecular composition.
“It was immediately obvious using our test that there were several suspicious samples, producing results that were consistent with the presence of substantial amounts of Robusta – far more than would be expected through unavoidable contamination,” said Dr Kemsley.
Two of the samples flagged as “suspicious” were bought in the UK. One contained 1.6 per cent Robusta and the other 21.7 per cent. Other UK samples had notable levels of 16-OMC but fell below the “suspicious” threshold.
Suspicious samples were also obtained from the US, Italy, France and Estonia. One US sample was a third Robusta, despite being labelled 100 per cent Arabica.