Istrian white truffles
The Istrian truffle has been known and highly prized since antiquity . In his Naturalis Historia, Pliny the Elder related about the truffle (Tuber in Latin). In the 1st century A.D., the idea that this precious fungus developed from the combined action of water, heat and lightning was passed on by way of the Greek philosopher Plutarch of Chaeronea. Various poets derived inspiration from this; one of them, Juvenal, explained the truffle as originating from a bolt of lightning struck by Jupiter near an oak (a tree held to be sacred to the father of the Gods). As Jupiter was also renowned for his prodigious sexual activity, truffles have also always been attributed with aphrodisiac properties. It was mentioned by Dioscorides, Plutarch and Pythagoras, among others. Not even Roman emperors, who attributed aphrodisiac properties to truffles, could resist their scent and flavour. Cicero called them the sons of the earth, while Pliny thought they were wonders of nature. The truffle continued to be highly valued throughout the Middle Ages and the Renaissance, especially among nobility and prelates. For certain „scientists“ of the period, its aroma was a sort of
„quintessence“ which produced an ecstatic effect on human beings. In the eighteenth century on all the European courts Istrian and Piedmont truffles were considered the most delicious food. The Istrian white truffles, alongside with the Piedmont truffle, had always been the most highly valued variety in the world.The white truffle or Tuber magnatum pico become known worldwide as the white truffle of Alba at the 1900s owing to a brilliant advertising campaign, which in turn resulted in the Istrian truffle being overlooked for a very long time. This “Istrian gold” was often discovered and exploited in Istrian forests, which was slyly kept a secret as the white Istrian truffle was put on tables throughout the world under many different names. However, the experienced traders and especially the true truffle connoisseurs would say that the Istrian white truffles, with all of its organoleptic properties – especially its intense scent and distinctive flavour, is still altogether the world’s best-quality truffle. This is the rationale behind the saying about the Istrian truffle: “Who tastes them once, becomes and remains for ever their ardent devotee. ”
Tuber magnatum is found in natural tartufaias in cool soils, that are little developed and lacking stagnant water. The soil consists of pelitic-sandstone rocks, sandstone-pelitic, sandstone, sandstone-limestone, limestone-clay, of the Miocene-Pliocene (Tertiary) period, and also the Pleistocene-Holocene (Quaternary) period.These soils always have a certain porosity that guarantee sufficient drainage.The texture of the soil can be open, open-sandy, open-limey, or open-sandy-limey. The ph reaction is from neutral to sub-alkaline (pH 7-8). The total limestone (CaCO3) varies significantly, depending on the type of substrate, which averages between 20 and 30%. The humus content has an average value of 3%, and the carbon to nitrogen ratio is around 10. Among the exchangeable bases, calcium is the most abundant.The natural tartufaias give good production in the years in which there is well-distributed precipitation, and most especially, when there is no drought during the summer months. An examination of the climate diagrams of Bagnouls and Gaussen illustrates that in such years, the curve for precipitation never falls below that of the temperature.The tartufaias are found from sea level to an altitude of 1000 m above sea level in the climate-band of the Pavari, between the cold sub-zone of the Lauretum and the warm sub-zone of the Fagetum.Tuber magnatum grows in symbiosis with various forest species depending on the environment, and on exposure to the air. Tuber magnatum can be found in various places, such as: In the debris of forest vegetation, with the British oak (Quercus peduncolata); linden (Tilia sp.), hazelnut (Corylus avellana), poplar (Populus alba, P. nigra, P. nigra var. italica), hornbeam (Carpinus betulus), roverella (Quercus pubescens). In planted poplar areas, and in rows along the streets, with the poplars and the willow trees (Salix alba, S. caprea, S. viminalis).At the bottom of humid valleys and along water courses, with the roverella (Quercus pubescens), the oak (Quercus petrea), the turkey oak (Quercus cerris), the hop hornbeam (Ostrya caminofilia).In hilly areas, where the shrubby vegetation consists mainly of brambles (Rubus sp.), wild plum (Prunus spinosa), Blood-twig Dogwood (Comus sanguinea), wild rose (Rosa canina), old man’s beard (Clematis vitalba), elder (Sambucus nigra), hawthorn (Crataegus monogyna e C. oxyacantha), firethorn (Pyracantha coccinea) and aromatic Spanish broom (Spartium junceum). Most of the natural tartufaias are found in these wooded areas, where the humidity never drops below a certain level during the summer.The previously-mentioned native broad-leaved plants, even if they are isolated in pastures or found in belts or in rows marking plots of land (or water courses) or at the side of rural roads, are capable of producing T. Magnatum, which at times can be collected even at considerable distance from the symbiotic plants.In Istria, the first fruiting bodies appear at the end of August; but since they emit little aroma and are invaded by insect larvae, they rot very quickly. As a result, they should absolutely not be collected. They are not fit for consumption. However, they do have some value, because they seem to have an important function in reproduction.The best white truffles for stimulating the senses are found when the average temperature is below 10 degrees C from the end of October to the end of December. These white truffles develop at a depth that can vary from a few cm to 30-40 cm, depending on the looseness of the soil, which also depends on the morphological regularity of the fruiting body.
TUBER MAGNATUM, PHYLOGEOGRAPHY (SSR)
Thanks to their organoleptic properties, white truffles are fungi appreciated worldwide. Their quality and market price depend on the species and, traditionally, the place of origin. Tuber magnatum Pico and T.melanosporum Vittad., producing the finest white and black truffles, respectively, are reported to be highly homogeneous genetically. Both are in fact supposed to have experienced a strong population bottleneck during the last glaciation and to be under an almost exclusive selfing . Consequently, the differences in the organoleptic properties in these truffles were attributed to environmental rather than genetic factors . However, more information on genetic structure and dynamics of these species are expected by using highly informative markers and an extensive sampling. In this work we have investigated whether T.magnatum populations are genetically differentiated by screening 9 polymorphic microsatellite loci on 370 T.magnatum samples, harvested all over the species distributional range.
Although they showed a high level of diversity, all samples turned out to be homozygous at all loci. More interestingly, the statistical analysis revealed the existence of a marked divergence among T.magnatum populations. Spatial autocorrelation and SAMOVA analyses, in fact, proved a geographic pattern, with southern and north-western populations forming well-separated groups. Furthermore, a comparison between RST and FST statistics, clearly disclosed the presence of a phylogeographic structure.
The genetic pattern uncovered in T.magnatum seems to follow the post-glacial expansion typical of most of the species with which this fungus must establish a mutualistic symbiosis.
CHEMICAL ANALYSIS OF TRUFFLES:
Chemical and nutritional Properties:
Somewhat surprisingly, truffles have a very high protein content, which is why they are often described as ‘vegetable meat’. White truffles and black truffles have the same chemical content and are made up of 73% water, the remaining weight comprising several types of minerals and organic substances such as calcium, potassium and magnesium.
In depth Chemical Analysis of Truffles:
Soil pH levels
There are in total over 100 different types of the fungal genus tuber. All are ectomycorrhizal, which means that’s they grow underground in symbiosis with the roots of certain trees. The two most popular truffles, tuber Melanosporum vitt. (black winter truffle) and the tuber Maganatum pico (white winter truffle) have mycorrhiza with oak trees and prefer a calcareous soil. This means that the soil where these truffles are usually found have the characteristic of a high pH level, which is caused by their high calcium carbonate (limestone) content. Bearing in mind that a neutral pH level is equal to 7.0 (pH < 7.0 is acidic, pH > 7.0 is alkaline) it is important that the soil pH level doesn’t go too high as this can interfere with tree growth which is dependant on the uptake of other nutrients such as iron.
The fresh truffles contain a number of organic molecules known as alcohols, aldehydes and ketones. The smell of the truffle is actually due to a molecule known as dimethylsulphide or CH3SCH3 (which is also found in asparagus) along with a collection of others. These molecules are also known as ‘volatiles’ and it is these volatiles that mycologists are interested in studying using head-space analysis, mass spectrometry and gas chromatography. Amongst the main varieties of truffles, the relative quantities of alcohols to aldehydes to ketones varies, but they all contain dimethylsulphide molecules.
What makes them smell
When the truffles are kept over a period of time the volatile sulphur compounds escape faster than the other molecules. It is the release of the dimethylsulphide (CH3SCH3) molecules along with CH3CH2CH2SCH3 and CH3CH=CHSCH3 into the air that give the truffles that strong pungent smell.
THE BIOLOGICAL CYCLE
Truffles must grow in symbiosis with shrubs or trees in order to produce the precious sporocarp; the exchanging of substances between the two partners (the truffle and the plant) takes place at the roots, in special formations known as mycorrhizae, which are structured differently for each species. The mycorrhizae are a sort of sleeve, formed by several layers of small septate tubes called hyphae; these twist themselves around the apexes of the terminal rootlets of the tree, forming a reticulum – or netlike structure – by working their way in-between the first layers of root-cells. The plant provides the fungus with various substances by way of this association, receiving mainly water and mineral salts in return. A large number of these hyphae – known collectively as mycelium – branch out from the reticulum into the ground in search of nutritive substances. Later, when all the environmental conditions are right, some of the hyphae intertwine to create the fruiting body in which the spores differentiate. The spores then germinate to form a new mycelium, which will itself create new mycorrhizae by combining with the young apexes of the roots. Unlike the fruiting bodies of epigean fungi, which grow above the ground, hypogean – or underground – fungi are not able to exploit air currents to scatter their spore. Evolution has therefore equipped them with a strong smell that becomes noticeable when the spores ripen, attracting insects and mammals which feed on the truffle and scatter its spores.
THE SENSORIAL ANALYSIS
The visual examination involves three aspects: making sure that the fruiting body is intact (a damaged truffle will deteriorate more rapidly, so it is not just a matter of looking good); the degree of cleanliness, as any residues of earth may conceal defects or imperfections, as well as making it less pleasant to look at; a purely subjective assessment of the specimen’s beauty and aesthetic appeal.
The texture of the truffle is then examined: a good truffle should have just a slightly elastic feel, and must be firm and compact, while being neither too hard nor excessively springy.
Finally, the smell: the aroma of a truffle is made up of an array of simple sensations of varying intensity and amplitude, and it is precisely this unique, alluring scent that has made it such a culinary success. The following terms are used to describe the aromatic composition of the Tuber magnatum: fermented, fungous, honey, hay, garlic, spices, damp earth and ammonia.
Storing fresh truffles at home:
To be enjoyed at their best, truffles should be consumed within a few days of being unearthed.
To help keep them longer, gently wrap them in absorbent paper (such as a paper towel) and store in a dry glass/plastic jar/container in the least cold part of the refrigerator. Do NOT remove soil traces on the tuber before wrapping.
White truffles and black truffles have a very strong aroma which will quickly impregnate any other foods in the fridge, so it’s important to store them in their own container.
The absorbent paper should be changed daily, and the jar/container must be kept dry.
During months when the outside temperature is cool (but not freezing), the storage container can be kept outside, making sure, however, that it is not left on sunlight.
White truffles can be stored for about one week, and the black varieties a few days longer.