Another Life: Not just for gourmets – why truffles are good for gardeners

Well – why not happy hares in Spain, frisking mainly on the plain? It’s January, time for that sort of thing. Besides, I was given a truffle tree for Christmas, and Spain is where I last savoured “something musky, fiery, savoury, mysterious” – Thackeray’s famous rave about the truffle in his French partridge pie.

My tree is a little hazel, about 40cm high, with the promise of growth in winter leaf buds at the tip. The secret, however, is at the roots, commercially inoculated with the mycorrhizal fungus Tuber aestivum, the precious white summer truffle.

Most plants have mycorrhizae as partners in the soil: the fungi feed the roots with phosphates in return for carbohydrates and sugars from the leaves. Those around many trees put up mushrooms as fruits, but the global truffles are formed underground or hidden among leaf litter. My hazel may or may not deliver the first truffle four or five summers from now – a great incentive to hang on for a few years more. [Ed: you can't be serious.]

Seeking wild truffles with the help of pigs or trained dogs is part of the mystique of the world’s most expensive fungi. (I shall be scrabbling on my knees, with a bit of help to get up.) A huge white truffle from the Umbrian region of Italy, weighing almost two kilos, was auctioned last month in New York for more than €50,000. But as chefs, foodies and travellers demand more truffles of any sliceable size, techniques for truffle “farming” have had mycorrhizal scientists racing to improve production.

The potential is all the greater as hotter summers limit the yield from the Mediterranean oak forests where truffles grow best. Swiss research ecologists have predicted fading harvests of Tuber melanosporum, the black winter truffle, as incessant summer droughts take effect. At Perigord, in southern France, Piedmont and Umbria, in Italy, and Aragon, in Spain, weather records have linked warm, dry summers with fewer winter truffles – a decline that has raised black-truffle prices as high as €2,000 per kilo.

At the same time, the Swiss pair noted, the changing climate has coincided with a general increase of fungi in Switzerland and the unexpectedly rich occurrence in southern Germany of Tuber aestivum, which sells for €6,600 a kilo. Hence, they concluded happily, the future climate could favour both natural and cultivated truffles in forests north of the Alps.

Tuber aestivum also grows in Ireland. It is hard to find without trained truffle hounds, but it fruits most commonly under beech trees in the limy soil of the midlands and sometimes under oak and birch. As Paul Dowding and Louis Smith showed in their splendid guide Forest Fungi in Ireland (published by Coford in 2009) it has a warty skin as black as the winter truffle – which is black all through – and needs a good scrub before eating. It has, says Louis Smith, a culinary expert on fungi, "a light, nutty flavour" and "a good strong aroma of earthy musty mushrooms and celeriac".

Coford, the government-funded National Council for Forest Research and Development, also sponsored Forest Fungi, a research project that has used truffle hounds to revisit recorded sites of Tuber aestivum. This was led by Dr Tom Harrington and Maria Cullen of the department of life sciences at Limerick University. At the first European conference on the summer truffle, in Vienna in 2009, they described a trial planting of 250 French- inoculated saplings of oak and hazel in a Co Limerick field and others in a broad-leaved plantation. It will take time to judge if the long-term yield and quality warrant commercial production.

Also at the big Vienna conference was Dr Paul Cullen, the entrepreneurial scientist heading Mycorrhizal Systems, based in Yorkshire, which produced my inoculated hazel. Along with marketing through garden centres, such as Johnstown, the company's network is global: its first Australian black truffle was harvested in 2012 from a three-year-old tree and its first Spanish one in 2013.

Finally, truffle oil – and I'm sorry to break this to you if you don't already know. An affordable bottle of truffle oil is highly unlikely to be what the label has led you to suppose. Our bottle from Italy, another family Christmas gift, readily declares its main content of good olive oil. But this appears above a photograph of white truffles and, across them, the word "Tartufo" (truffle) in the label's biggest letters. In the middle, tiny and almost lost in the truffle image: "ed aroma al" – "and smell of".

“Aroma truffe 1%”, an ingredient listed on the back, could have been more specific. Chances are it is a dash of 2,4-dithiapentane, a laboratory compound that simulates, after a fashion, the heady scent of truffle. Some chefs would shrug and lash it on; others disown it and throw up their hands. I’ll just wait – and wait – for a whiff of the real thing.