Summer Truffle
Tuber aestivum
Also called burgundy truffle, black summer truffle, scorzone
A widespread hypogeous ascomycete with a black exterior of large, coarse pyramidal warts and a pale hazel-brown interior broadly marbled with white veins.
Overview
The Summer Truffle is the most widely distributed black-skinned Tuber in Europe and the one most often turned up by accident in ordinary beech and oak woodland. Its exterior is unmistakably truffle-like — a hard black knobbly ball — but the interior gives it away instantly, staying a pale biscuit or hazel brown even when fully ripe.
Forms fruiting later in the year with a darker gleba and slightly different vein pattern have long been separated as the Burgundy truffle, Tuber uncinatum. Genetic work has shown these to be the same species expressing seasonal and ecological variation, so the two names are now generally treated as synonyms of Tuber aestivum.
As a member of Tuberaceae the species fruits entirely underground, ripening a closed body in which spores form inside asci. It is the most ecologically tolerant of the European truffles, occurring across a much greater range of climate and soil than either the Perigord or Alba species.
How to identify it
Fruiting body
Globose to irregularly lobed, commonly 3-10 cm across, hard and heavy for its size. The peridium is black to blackish brown and armoured with large, coarse, prominent pyramidal warts, each typically four- to six-sided with a ridged apex — noticeably bigger and rougher than those of the Perigord truffle, giving a strongly sculpted, almost armadillo-plated look.
Interior (gleba)
Whitish in immature bodies, ripening to pale hazel, biscuit or greyish brown — never purple-black. It is crossed by conspicuous, broad, white, branching sterile veins that are more widely spaced than in T. melanosporum, producing a coarse marbling clearly visible to the naked eye.
Aroma and texture
The smell is nutty, earthy and mushroomy rather than pungent, and is markedly milder than that of the winter black truffle. The flesh is firm and slices cleanly with a fine-grained cut face.
Spores
Spores form in asci, usually one to four per ascus, and are broadly elliptical, yellow-brown, and ornamented with an irregular net of ridges (a reticulum) rather than free spines — a reliable microscopic separator from Tuber melanosporum.
Where and when it grows
Summer Truffles grow in calcareous, well-drained woodland soils, often on slopes, in beech hangers, oak woods, hazel coppice and mixed plantings. Associated trees include beech, several oaks, hazel, hornbeam, lime, birch and occasionally pines, and colonies can occur under quite young trees.
The range is the widest of any European truffle, extending from Spain and Italy north to Britain, Sweden and Poland, and east into eastern Europe and parts of the Near East. Fruitbodies form in spring and early summer, mature from midsummer onward, and later-fruiting populations continue into late autumn or early winter, which is where the Burgundy truffle name is applied.
Ecological role
Like other members of the genus, Tuber aestivum is ectomycorrhizal, forming a hyphal mantle and Hartig net on the fine roots of its broadleaved hosts and trading soil-mined water and mineral nutrients for tree carbohydrates. Its broad host range and tolerance of cooler, wetter conditions explain its exceptionally wide European distribution.
A weak bare zone sometimes forms around colonised trees, but it is far less pronounced than the scorched ring of the Perigord truffle. Spore dispersal relies on animals: mice, voles, squirrels, deer, boar and beetles excavate ripe bodies, and spores survive gut passage to be deposited elsewhere, where they can colonise new root tips.
Similar species
Tuber melanosporum is separated most reliably by cutting: its gleba ripens deep purple-black with fine, dense veins that often redden, while T. aestivum stays pale hazel-brown with coarse, widely spaced white veins. Its warts are also smaller and neater. Tuber mesentericum is very similar externally but usually shows a distinct cavity or fold at the base, a darker gleba and a sharply different, strongly phenolic aroma.
Tuber brumale has finer, lower warts and a greyer gleba with fewer, thicker veins. Earthballs (Scleroderma citrinum and relatives) can be mistaken for truffles when half-buried, but their rind is ochre-yellow and coarsely scaly rather than black and pyramidal-warted, and their interior turns solid black-purple and then powdery with no white vein network.