THE most expensive coffee in the world is shit. That is not an opinion, it is a fact. To make Kopi Luwak you must, of course, start with high-quality beans. But then you have to feed them to palm civets, wait while they pass through the animals" guts (having their fleshy exteriors digested as they go) and be ready to collect them when they come out of the other end. The result, when cleaned, fermented, dried, roasted, ground and brewed, sells for as much as $80 a cup. The reason for this apparently ludicrous price is the sublime effect on the beans" flavour of the chemical reactions they undergo in a civet's stomach. Given that price, a lot of counterfeit and adulterated Kopi Luwak gets peddled as the real thing. And until now there has been no reliable way to detect it. A purchaser may think from the flavour that he has been duped, but he cannot prove it. Eiichiro Fukusaki of Osaka University, in Japan, plans to change that. As he describes in the Journal of Agricultural and Food Chemistry, he and his colleagues in Japan and Indonesia have developed a chemical test which, they believe, can reliably detect essence of civet in coffee. Dr Fukusaki's quest began with many piles of civet faeces, as well as undigested coffee beans from plantations in Bali, Java and Sumatra, all of which he treated by roasting them at 205°C and then grinding them up. Instead of popping them into a percolator at this point, though, he mixed them with distilled water, methanol and chloroform to extract the sorts of chemicals that give coffee its flavour. He then ran the extracts through a gas chromatograph and a mass spectrometer, to see what was in them. The crucial giveaways of Kopi Luwak turned out to be four substances: citric acid, malic acid, pyroglutamic acid and inositol. The real McCoy had much more of the first two than similar beans that had not undergone trial by civet, and the ratio of the last two was reliably different. Moreover, the differences were big enough that even a 50:50 mixture could be identified, enabling adulterated Kopi Luwak, as well as stuff masquerading as it, to be detected. Whether lower levels of adulteration than that can be detected remains to be seen. But Dr Fukusaki's method, if widely adopted, would certainly weed out the worst excesses of the fraudulent Kopi Luwak market. On the other hand, it might inspire counterfeiters to try tweaking their products with laboratory chemicals. And if that resulted in the same flavour as the genuine article it would relieve the civets of their onerous task and open up the drinking of Kopi Luwak to mere mortals.