Chestnut bolete or Bitter bolete

The cap of the bitter bolete reaches 4 to 15 centimeters across, and in especially good years you'll find real giants up to 20 centimeters. When young it is neatly hemispherical, opening with maturity to convex and later almost flat and spread out. The cap surface is dry, delicately velvety or finely felty to the touch in young mushrooms, but becomes smooth with age. The color palette ranges from light hazel and coffee brown to a warm ochre-brown, which especially heightens the deceptive resemblance to porcini.

Cap 3–12 cm, hemispherical in young mushrooms, then flat-convex or flat. Color chestnut-brown, reddish-brown, sometimes lighter — hazel. The surface is dry, finely felty to the touch, and may crack slightly in old mushrooms. The skin does not peel off.

Under the cap lies a tubular hymenophore, which is the main giveaway of this impostor. In very young mushrooms the tubes and pores are whitish, which, once again, recalls porcini, but very quickly they take on a characteristic dirty pink or flesh-pink hue. It's this pinkness that firmly sets the bitter bolete apart from true porcini, whose hymenophore can be white, yellow or olive, but never pink. When pressed or damaged, the pores often turn brown, developing rusty brown spots.

Pore surface of tubes, white at first, then yellowish to straw-colored. Pores small and round. They do NOT turn blue when pressed — this is the key difference from its relative Gyroporus cyanescens.

The stem of the bitter bolete is massive and sturdy, 4 to 10 centimeters tall and up to 3 centimeters thick. It is swollen and club-shaped, especially thickened at the base, which makes the mushroom look stocky and dependable. The stem is colored in ochre-brown tones, lighter at the top and darker toward the base. The most important diagnostic detail is the net pattern: unlike porcini's delicate pale netting, the bitter bolete's net is distinct, coarse and dark, chocolate-colored or even blackish, and clearly visible to the naked eye. There is no ring and no volva at all.

Stem 4–8 cm tall, 1–3 cm thick, cylindrical or slightly tapering toward the base. Same color as the cap or a little lighter. The surface is finely felty. The most distinctive feature: in mature mushrooms the stem is hollow inside, with uneven chambers — like dried bamboo.

The flesh of the bitter bolete is thick, dense and fleshy, white or slightly cream-colored. When cut it mostly stays unchanged, although in some specimens it may turn faintly pink on exposure to air. There's none of the bluing typical of many boletes. But the flesh's main feature lies not in its color but in its taste: it is extraordinarily, unbearably bitter, like bile or quinine. It's this bitterness, which cooking doesn't destroy, that makes the mushroom unfit for the table.

Flesh white, brittle, does NOT change color when cut (an important feature — other boletes with a chestnut cap often turn blue or pink). Hollow in the stem of mature mushrooms.

The smell of the bitter bolete is faint and fairly nondescript, typically mushroomy, with no sharp or unpleasant notes. Unlike the taste, the aroma carries no warning at all and may well seem pleasant. That's exactly why you shouldn't rely on your nose to identify this species — the deceptively mild smell only adds to its overall resemblance to the noble porcini.

The smell is faint, pleasantly mushroomy with a hint of nut. The taste is mild, sweetish, reminiscent of a real chestnut.