About Boletus edulis Bull.
The scientific name of this species is Boletus edulis Bull. Its cap reaches 8–30 cm (3–12 in) wide, and occasionally grows larger. When moist, the cap surface is viscid; young caps are convex, and they flatten as the mushroom ages. Cap colour is generally reddish-brown, and sometimes has a paler margin. The stipe grows up to 8–25 cm (3–10 in) tall and 2–7 cm (1–3 in) thick, and it is quite large relative to the cap. Young stems are usually enlarged at the base, and become more cylindrical with age. The stipe surface is finely reticulate on the upper portion, or sometimes across its entire surface. The stem flesh is sometimes dark yellow near the base. The cap undersurface is made up of thin tubes that produce spores; these tubes are 1 to 2 cm (1⁄2 to 3⁄4 in) deep, whitish when young, and mature to a greenish-yellow colour. The small angular pores do not stain when bruised, with roughly 2 to 3 pores per millimetre. When young, pores are white and look like they are stuffed with cotton, which is actually made of mycelia; as the mushroom ages, pores change colour first to yellow and later to brown. The spore print of Boletus edulis is olive brown. Fruit body flesh is white, thick, and firm when young, and becomes somewhat spongy with age. When bruised or cut, the flesh either does not change colour, or turns a very light brown or light red. Mature specimens typically weigh about 1 kg (2 lb 3 oz). A very large specimen collected on the Isle of Skye, Scotland, in 1995 weighed 3.2 kg (7 lb 1 oz); its cap measured 42 cm (16+1⁄2 in) wide, and its stipe was 18 cm (7 in) tall and 14 cm (5+1⁄2 in) wide. A similarly sized specimen found in Poland in 2013 received international news coverage. Spores of Boletus edulis are elliptical to spindle-shaped, measuring 12–17 by 5–7 μm. Spore-bearing cells called basidia are produced in a layer that lines the tubes, with their ends facing toward the center of the tube; this cell layer is technically known as the hymenium. Basidia are thin-walled, most attach to four spores, and measure 25–30 by 8–10 μm. Another cell type present in the hymenium is cystidia: larger sterile cells that protrude past the basidia into the hymenium lumen, and act as air traps to regulate humidity. B. edulis has pleurocystidia (cystidia located on the face of a pore) that are thin-walled, roughly spindle-shaped to ventricose, and measure 30–45 by 7–10 μm. The stuffed appearance of the young hymenium is caused by cheilocystidia, cells found on the edges of the pores. The hyphae of B. edulis do not have clamp connections.
Fruit bodies of Boletus edulis can grow singly or in small clusters of two or three specimens. This mushroom grows in habitats dominated by pine (Pinus spp.), spruce (Picea spp.), hemlock (Tsuga spp.) and fir (Abies spp.) trees; other host trees include chestnut, chinquapin, beech, Keteleeria spp., Lithocarpus spp., and oak. In California, porcini (the common name for this species) have been collected in a range of forest types, including coastal forests, dry interior oak forests and savannas, and interior high-elevation montane mixed forests, up to an altitude of 3,500 m (11,500 ft). In northwestern Spain, they are common in scrublands dominated by the rock rose species Cistus ladanifer and Halimium lasianthum. In the Midi region of south-west France, the mushroom is particularly favoured, and is locally called cèpe de Bordeaux after the town from which it is traded to northern areas and abroad. Boletus edulis has a cosmopolitan distribution, concentrated in cool-temperate to subtropical regions. It is common in Europe, ranging from northern Scandinavia south to the southern extremes of Greece and Italy, and in North America, where its southern range extends as far south as Mexico. It is well known from the Borgotaro area of Parma, Italy, where it holds PGI status. Its European distribution extends north to Scandinavia and south to southern Italy and Morocco. In North America, it can be found from May to October in inland areas, and from August to January on the West Coast. In China, the mushroom occurs from northeastern Heilongjiang to the Yunnan–Guizhou Plateau and Tibet. It has been recorded growing under Pinus and Tsuga in Sagarmatha National Park in Nepal, as well as in the Indian forests of Arunachal Pradesh. In West Asia, the species has been reported from the northwest forests of Iran.
Some progress has been made toward cultivating Boletus edulis, including mycorrhization of rockrose shrubs boosted by helper bacteria.
As the species epithet edulis (Latin for edible) indicates, Boletus edulis is an edible mushroom. Italian chef and restaurateur Antonio Carluccio described it as "the wild mushroom par excellence", and praised it as the most rewarding of all fungi for cooking, due to its flavour and versatility. It is considered a top-choice edible, particularly in France, Germany, Poland and Italy, and was widely written about by Roman writers Pliny the Elder and Martial, who ranked it below the highly esteemed Amanita caesarea. When served suilli instead of boleti, the disgruntled Martial wrote: sunt tibi boleti; fungos ego sumo suillos (Ep. iii. 60), which translates to "You eat the choice boletus, I have mushrooms that swine grub up." The flavour of porcini is described as nutty and slightly meaty, with a smooth, creamy texture, and a distinctive aroma that resembles sourdough. Young, small porcini are most valued, because large porcini often host insect larvae (maggots), and become slimy, soft, and less flavoursome as they age. To collect fruit bodies, harvesters hold the stipe near the base and twist gently. Cutting the stipe with a knife may leave a leftover section that rots and risk destroying the mycelium. Peeling and washing are not recommended. Fruit bodies are highly perishable, largely due to their high water content (around 90%), high enzyme activity, and the presence of a community of microorganisms. Caution is needed when collecting specimens from potentially polluted or contaminated sites, because multiple studies show fruit bodies can bioaccumulate toxic heavy metals including mercury, cadmium, caesium and polonium. Bioaccumulated metals or radioactive fission decay products act like chemical signatures; chemical and radiochemical analysis can be used to identify the origin of imported specimens, and for long-term radioecological monitoring of polluted areas. Porcini are sold fresh in markets during summer and autumn in Europe and Russia, and sold dried or canned at other times of the year, distributed worldwide to countries where they do not naturally grow. They are enjoyed raw, sautéed in butter, ground into pasta, used in soups, and included in many other dishes. In France, they are used in recipes such as cèpes à la Bordelaise, cèpe frits and cèpe aux tomates. Porcini risotto is a traditional Italian autumn dish. Porcini are a feature of many cuisines, including Provençal and Viennese. In Thailand they are used in soups and eaten blanched in salads. Porcini can be frozen, either raw or after cooking in butter. Their colour, aroma, and taste deteriorate noticeably after four months of freezing. Blanching (or soaking and blanching) as a processing step before freezing can extend freezer storage life to 12 months. They are also one of the few mushroom species sold commercially as pickled product.
