The Biology of . . . Truffles

Expensive and delectable, truffles are one crop modern agriculture can't tame

By Robert Kunzig
Nov 1, 2000 6:00 AMApr 12, 2023 1:36 PM


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"Truffles are a mystery, and let's hope they stay that way along time. Some people, when they smell one . . . " Jean-Louis Fioc takes a deep breath, and an expression of exaltation passes over his weathered face from mouth to gray temples. "You cannot define the smell of a truffle. It is magic."

It is mid-April in the Rhône Valley, just north of Provence in the Drôme region, and the day is magical enough. Gusts of mistral have cleared the sky, the sun is strong but not yet oppressive; snow fell two nights ago on the distant mass of Mont Ventoux. We have walked through Fioc's fields of thyme and blooming rosemary to get to this small grove of scrubby oak trees. The truffle season ended last month, but we— or rather, Fioc's dogs— are looking to scare up a few last specimens of the round, dark-brown, warty, subterranean, and absurdly expensive mushroom.

Before World War I, France produced as many as 1,000 tons a year of black Périgord truffles, the finest kind. Even ordinary French folk stuffed their Christmas turkeys with them. Now the annual harvest is about 30 tons, and there are many more hungry mouths. The wholesale price last winter hovered at $200 a pound.

Truffles do not fit in this age of genetically engineered corn and soy. Trufficulture cannot be mechanized. Really, truffles cannot be "grown" at all. A truffle farmer does not plant truffles, he plants oak trees— truffles grow only near the roots of certain trees (evergreen oak and pubescent oak are best). Five years later at the earliest, 10 years later more likely, the farmer-hunter paces around the grove on a cold winter day with an animal— a pig traditionally, but a trained dog most frequently— that can smell buried truffles. Sometimes he finds a lot; sometimes not. "You can't count on truffles," says Fioc. "Maybe a tree will produce and maybe it won't, but if it doesn't you have only your eyes to cry."

Raising truffles is not quite as chancy as it used to be, though, thanks in part to Gérard Chevalier of the National Agricultural Research Institute in Clermont-Ferrand. In the early 1970s Chevalier and his colleagues figured out how to inoculate the roots of tree saplings with truffle spores, thus increasing the chances that the trees would produce truffles. When a truffle spore comes into contact with one of the hair-thin rootlets that fan out under an oak, it sends out long, microscopically thin filaments that wrap around the root. Under magnification the root tip comes to look fuzzy and slightly swollen, like the end of a cotton swab. That swollen tip is called a mycorrhiza, from the Greek words meaning "fungus root." It is part of both truffle and tree.

Like all fungi, truffles are unable to synthesize sugars and other carbohydrates; they have to get them from plants. Ordinary white mushrooms colonize dead plant matter, which is why they are readily grown on compost and on an industrial scale. Other fungi, such as mildews, are parasitic; they suck carbohydrates out of plant leaves and give nothing in return. Truffles are nicer. They draw carbohydrates from the tree and use them to construct filaments that push through the soil in search of other rootlets, in an ever-expanding invisible web of fungus— but they also give something back. The mycorrhiza with their filaments are far better than an uncloaked rootlet at collecting nutrients for the tree; initially, at least, oak trees grow better, not worse, when infested by truffles. "It is an entente cordiale," says Chevalier. No one has ever managed to grow a truffle in the lab, without a tree.

At some point, possibly when the web under the tree reaches a certain density, and typically in May, a sex act with profound culinary consequences takes place. Whether two different filaments, one male and one female, have to coalesce, or whether an edible black truffle fruit springs forth from a single hermaphroditic filament is not clear. "Mushroom sex is infernal; it's very complicated," says Chevalier. Later, in the heat of August and September, the young truffles go on a growth tear that brings their weight to an ounce or two and sometimes to as much as a pound. Then they slow down and start to ripen. Their interior turns black with white veins. They become, in effect, pockets of spores, and they begin, round about December, to smell quite strong.

Smell is essential. Without it, a truffle would rot in place and not fulfill its function of spreading seed. With the smell, a truffle attracts animals. Burrowing rodents gobble it and wander off to excrete the spores elsewhere, ideally under an uncolonized oak. According to Thierry Talou, a chemist at the National Polytechnic Institute of Toulouse, the single most important component of a truffle's smell is dimethyl sulfide, which is also the active ingredient in cabbage. "Some people like the smell; others don't at all," says Talou. "It's about fifty-fifty."

Pigs like the smell, a lot. In 1981 some German researchers discovered that black truffles contain androstenol, a sex hormone found in the saliva of male pigs (and under the arms of male humans). This led to all kinds of speculation about pigs, sex, and truffles, which Talou proved was hogwash. After identifying the chemical components of truffle aroma, Talou succeeded in synthesizing the nine most important ones, which do not include androstenol, and mixing them into a chemical cocktail that would fool most human noses. (Pébeyre, a truffle merchant in Cahors, now makes a truffle oil with this synthetic aroma.) In one of a series of experiments in the early 1990s, Talou buried samples of the synthetic aroma at various points under an oak tree, real truffles at other points, and samples of androstenol at still others. He found that pigs ignored the androstenol. On the other hand, they grubbed for real truffles and the synthetic scent with equal enthusiasm— in the latter case, they had to be restrained from eating the scented dirt and rocks. Their hunger seems not to be sexual in nature.

All pigs, male and female, love to eat truffles, and that is one reason pigs are falling out of favor at harvest time. "They eat a rather significant number," says Talou. "Also, it is not easy to transport a pig." Dogs are less voracious but often less efficient. For years now Talou has been trying to develop an electronic truffle detector, and next month he will be testing his latest model. At its heart is a microchip bearing tiny squares of a conducting polymer whose resistance to an electric current is altered when it comes into contact with truffle volatiles. If it works, Talou thinks there are hundreds of people who would be willing to pay, say, $5,000 for his gizmo.

Fioc is an unlikely customer. His dogs can smell pea-sized truffles under a foot of dirt. While we are watching, Daisy, a grizzled 10-year-old collie, begins to paw methodically under one of the trees. Gently shoving her aside, Fioc deepens the hole and soon extracts what looks to be a dark dirt clod, about an inch and a half across— a nice size. Later, after Daisy has graced us with a second, smaller truffle, and we have sat down at one end of the grove to discuss truffles, life, and the omelette Fioc's wife will be making later, my 4-year-old quietly removes the larger fungus from the basket and feeds it to the collie. Quickly I do the arithmetic: That was a $15 dog biscuit.

It doesn't spoil Fioc's day. The dogs are recovering from the hunt now, lying in the flowered grass and panting contentedly. "Look at them, how happy they are!" says Fioc. "They're teaching us something." Maybe truffles, elusive and indomitable as they are, can teach us something too— gratitude for small blessings, fungal and otherwise; gratitude, too, for the little knots of beauty that can sometimes lurk inside hideous packaging. With his pocketknife, Fioc strips a few cool, chalky, odoriferous flakes from the remaining dung-brown truffle. We sniff them meditatively. Then we eat them raw.

Want to dig up more on truffles? Visit the oak-leaf-wallpapered Web site of the French Federation of Trufficulturists (La Fédération Française des Trufficulteurs) at (English-language version available).

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