Food and agriculture

Coralie Fenwick: Good evening. When I tell people I study truffles, they tend to picture someone in a smart restaurant with a silver grater. In fact most of my working life has been spent kneeling in a field of rather ordinary-looking young oak trees, waiting for something to happen underground. Coralie Fenwick: A truffle, for anyone who hasn't met one, is the fruiting body of a fungus that lives in partnership with the roots of certain trees. The fungus helps the tree to take up water and minerals, and the tree feeds the fungus with sugars. Unlike a mushroom, though, a truffle stays below the surface, so it can't release its spores into the wind. It depends instead on being dug up and eaten by an animal, which is why, once it's ripe, it gives off such a powerful smell. Coralie Fenwick: Twelve years ago our research station planted eight hundred oak seedlings whose roots had been treated with truffle spores in a nursery. The textbooks told us to expect a first harvest after about six years. We waited six years, then seven, then eight. And the first sign that anything was going on wasn't a truffle at all. It was a circle of bare, scorched-looking earth around the base of a few trees, where the fungus holds back the grass and other plants. Growers call it a 'burn'. I remember the whole team standing round one of those bald patches as if it were a masterpiece. Coralie Fenwick: So how do you find something buried ten centimetres down? Traditionally with a pig, and people assume pigs went out of fashion because they eat the truffles. They certainly try, and a large pig takes some holding back. But the bigger problem, for a research plantation at least, is that a pig roots up the ground so thoroughly that it tears apart the fine threads of the fungus in the soil, and you can ruin a patch for years. So we use dogs, which dig far more politely and will happily work for a cube of cheese. Our best dog, a retired sheepdog called Wick, was first trained on cotton wool soaked in truffle oil, until somebody pointed out that most of the truffle oil sold in shops has never been anywhere near a truffle; its flavour is made in a laboratory. Wick had to be retrained from scratch on real truffle peelings, which cost us a small fortune. Coralie Fenwick: The other lesson was about ripeness. I'd assumed you could judge it from the colour of the flesh, which darkens as a truffle matures. But a truffle can look perfect and have almost no scent. The only reliable test is the one the dog applies: he simply walks past unripe truffles. Which, of course, is exactly what the fungus intends. There's no point in being eaten before your spores are ready. Coralie Fenwick: People always ask about the money, because truffles fetch such absurd prices. What I value more is that a field like ours forces you to think in decades. It rewards the person who planted it, if at all, long after the grant that paid for the trees has run out. That kind of patience can't be trained into anyone. Not even a dog.