Truffles are the fruiting bodies of soil fungi that live in a symbiotic relationship with the feeder roots of trees. The combination of the fungus and the root is called a mycorrhiza (plural: mycorrhizae). There are some 5000 species of truffle-producing fungi though only 70 of those produce truffles that are edible by humans.
The truffle contains the spores (analogous to seeds) of the fungus and when the spores are ripe the truffle develops characteristic aromas that attract animals to dig them up and eat them. The spores pass through the animal's digestive tract and are deposited in the scat where they can germinate and begin a new the symbiotic relationship with appropriate host trees. Each species of truffle-producing fungi will form a relationship with a limited number of tree species, however trees are less selective in their hosting of different soil fungi on their roots.
Traditionally truffles are harvested from woodlands, however several species can now be cultivated. Host tree seedlings are inoculated with truffle spores in the nursery before planting out in the field, and production and harvest begins five to seven years later. Specially trained dogs are used to locate the truffles which are found in the top 30cm of the soil profile.
The genus Tuber produces the most highly prized truffles in Europe, and several species are sold in local markets at various times of the year. Two species of truffles are particularly highly prized - the Italian white truffle (Tuber magnatum) commands the highest prices but has not yet been successfully cultivated, while the French black truffle (T. melanosporum) is both highly valued and has been cultivated. Table 1 lists some of the commonly used truffles from around the world.
|Tuber magnatum||Italian white truffle|| |
The most expensive truffle, always added to food after cooking. These truffles have not yet been cultivated.
|Tuber melanosporum|| |
French black truffle
The most highly valued black truffle, widely traded and now cultivated around the world.
These two truffles differ only in their geography and season. They are milder than the black truffle.
Italian whitish truffle
The whitish truffle is much milder than the white or black truffle but still pleasant and widely used. It has been cultivated and grows more easily than the black truffle in cultivated orchards.
Bagnoli truffle (Italy)
Lorraine truffle (France)
Enjoyed in localised natural production areas, it can have very strong sometimes bitter odours.
smooth black truffle
Found mainly in Italy, this truffle is milder than the white truffle but still prized for its pleasant garlicky aromas.
Tuber indicum complex
includes T. sinense, T. himalayense
Several truffles are found in China, with some disagreement about their quality and the methods of harvesting. They routinely attract far lower prices than the European truffles.
Frequently found as a contaminant in black truffle orchards across Europe, New Zealand and eastern Australia, the aromas can be quite phenolic and unattractive. The fungus is an aggressive competitor to T. melanosporum.
Oregon white truffle
Oregon June truffle
Oregon black truffle
Native to north America, these truffles are locally prized for their pleasant aromas and are utilised in similar ways to their European counterparts.
|desert truffles|| |
These are likely to be the truffles described in ancient texts. They are found around the Mediterranean and Middle East. Many have mild flavours and are readily infused with the flavours of cooking.
It is possible to confuse different truffle species in the market. Testing to determine the type can be done using DNA analysis or microscopic inspection.
Care must be taken when inoculating trees to ensure the correct truffle spores are used. Different species of truffle, and indeed other fungi, can compete in the soil resulting in reduced yield of the desired truffle. Tuber brumale, in particular, is very competitive.
While truffles have been eaten and written about for centuries, it is only since the late 1960s that systematic research has been undertaken on the conditions needed for growing truffles in cultivated orchards. Hence our knowledge is still developing. Presented here is the best available information at present for the conditions required in Manjimup, Pemberton and Northcliffe where black truffles are being cultivated. Much of the information may be applicable to other areas and growers are advised to consult with local agronomists and horticultural personnel who have a specific interest in truffle production, as well as undertaking their own research before deciding on a course of action.
The life cycle of the truffle is somewhat different to that of the more familiar above-ground mushrooms. Whereas mushrooms develop rapidly after rain events in the appropriate season, truffles are initiated in summer and early autumn and continue to grow before maturing in the cold winter months. Hence, by the time a truffle is mature (and aromatic) enough to attract the attention of a well-trained dog, it will have been developing underground for up to eight months.
If truffles are harvested or even disturbed before they have developed the quintessential aromas associated with maturity, they will not continue to mature or develop and are likely to rot. Current evidence suggests that as the truffles grow in late summer and autumn, they continue to derive all their nutrients from the tree via mycorrhizae.
Western Australian truffle industry
The Western Australian truffle industry is based on the French black truffle or Périgord truffle (Tuber melanosporum) grown in association with oak trees (mainly Quercus robur and Q. ilex) and hazelnut trees (Corylus avellana). Seedlings are inoculated with fungal spores from mature truffles before being planted out into orchards (or trufferies). Truffle production usually begins five to seven years after planting.
The first commercial plantings of truffles in Western Australia occurred in 1997, with the first harvest in 2003. While black truffles are successfully cultivated around Manjimup and Pemberton, it is not known whether production will be successful in other areas. Inoculated oak and hazelnut trees have been planted in the Perth Hills and at Toodyay, north-east of Perth, as well as Margaret River, Busselton, Nannup, Donnybrook, Bridgetown, Walpole and Denmark.