FYI: They're the delicacy of choice for the world's gastronomic glitterati, but what exactly are truffles? Expensive, that's what. So dear that dogs trained to sniff them out are often dognapped (or even poisoned) by rivals, and sniffer pigs are muzzled so they can't eat them. The best truffles - the white variety (Tuber magnatum pico), most commonly found in Italy - are known as white gold, even though they are worth six times more than gold. The most expensive was a 1.51kg Alba white truffle snapped up by Sir Gordon Wu Ying-sheung at auction for HK$1.25 million last month. The truffle is a rare type of mushroom or fungus that grows underground. It's circular, or misshaped if grown near stones or tree roots, and has a distinctive aroma that grows on the uninitiated. Larger truffles grow to the size of a cricket ball. They sprout in early summer and, given sufficient rain, begin to swell, ready for the season, from October to January. They come in three main types. The white truffle hails from Piedmont, northern Italy, but they crop up occasionally in Croatia and Slovenia. The most fabled variety is the Alba white, named after the town where an annual truffle fair and auction is held, an olfactory event during which the smell halts the squeamish at the town gate. The scent of truffle is not always pleasant, reportedly smelling like petrol, farmyards, musk, garlic or runny cheese. Some say it smells like death and sex mixed together, while others claim it's akin to the intestine of a pig on heat, old socks or the post-match dressing room. Nice. There's also the black Perigord truffle, grown mainly in France but more recently being farmed in Tasmania, Australia. Then there's the summer or Burgundy truffle, found mainly in Britain, which grows 25mm underground, allowing experts to detect them simply by walking near trees, apparently in espadrilles. Such truffles can fetch up to #400 (HK$6,100) a kilogram. In contrast, the white and black truffles are buried as deep as 10cm, hence the need for dogs, such as labradors, and pigs. (Lustful female pigs, to be precise: the truffle smells like the pheromone of a male pig). Sometimes, moles and rabbits unearth the delicacy, leaving it exposed near the surface for humans to chance upon. This is nature's equivalent of winning the lottery without even buying a ticket. China is also getting in on the act by 'farming' truffles, with some unscrupulous European chefs using the supposedly inferior tasting, more chewy and cheaper Chinese truffles. Truffles are increasingly rare, largely because it is hard to farm them. Hard, but not impossible. About 70 per cent of truffles are farmed, often cultivated near trees in plantations. Of course, many French and Italian peasants deny this - the truffles are found, they say, not cultivated and are therefore a windfall (not taxable). France's annual truffle production has fallen from 800 tonnes to just 12 tonnes in the past century, with prices now reaching #2,700 a kilogram. Adding to their cost is the fact truffles don't keep very long (roughly a week in the fridge wrapped in silver foil). And you can't pickle truffles, which is why top-end restaurants fly them in. Andy Needham, head chef of London's Zafferano, should know. He paid #28,000 for a truffle, put it in a chilled safe and went on holiday. Guess what had happened by the time he came back? Myth also has it that the truffle is a good aphrodisiac, perhaps because whoever is offering it is obscenely rich. After all, it can't be because of its smell - the whiff of old socks or the intestine of a sow on heat can hardly enhance the mood.