Brown birch 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 5–15 cm across, at first spherical or hemispherical, later cushion-shaped. The surface is smooth or slightly wrinkled, dry or a little sticky in wet weather. Color ranges from grayish brown to dark brown, more rarely almost black.

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.

The hymenophore is tubular. The tubes and pores are white, small in young mushrooms and wider in mature ones. When pressed, the pores turn slightly brownish, but there's never any bluing: unlike in the red-capped scaber stalks, the flesh doesn't blue even at the stem base.

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 8–18 cm tall, 1.5–3 cm thick, cylindrical, fairly long and slender compared with the cap. The surface is white or grayish, densely covered with dark, fibrous scales — the hallmark of the genus Leccinum. The stem is firm and fibrous.

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.

The flesh is firm and white; when cut it doesn't change colour or turns slightly pinkish, and after a few hours may become a little greyish or brownish. It darkens to grey-black only when cooked. The taste is mild and neutral. The cap skin doesn't peel.

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 unobtrusive, pleasant and typically mushroomy. The aroma intensifies with cooking. When dried, the brown birch bolete takes on a rich scent that falls short of porcini but is noticeably better than most other pored mushrooms.