Porcini or Oak bolete

Cap 7–30 cm across, spherical or hemispherical in young mushrooms, becoming cushion-shaped and spread out over time. The color varies from light brown to dark chestnut or reddish brown depending on light and forest type: caps are darker in spruce woods and lighter in pine forests.

The cap surface is dry, smooth or slightly wrinkled, and can be a little sticky in wet weather. The margin is even or slightly wavy, inrolled in young mushrooms. The skin doesn't peel.

Cap 6–20 cm, hemispherical in young mushrooms, then flat-convex to cushion-shaped. The color varies: brown, yellow-brown, olive-brown, darker in the center. The surface is dry, slightly sticky in wet weather; in mature mushrooms it may crack finely into soft patches.

The hymenophore is tubular and separates easily from the cap flesh. In young mushrooms the tubes are white, later turning yellow; in mature ones they're yellow-green or olive. The pores are small, round, uniform in color and don't change color when pressed.

The spore-bearing surface is made of tubes, with a slight notch near the stem. The color is rich yellow (a buttery yellow — hence the genus name "butyri"). The pores are small and round. When pressed they may turn slightly blue, especially in mature mushrooms.

Stem massive, 5–20 cm tall and 3–10 cm thick, bulbous or club-shaped in young mushrooms, later cylindrical. Color from whitish to light brown. The surface is covered with a characteristic white or cream net pattern, most distinct in the upper part of the stem.

There's no ring and no volva. The base of the stem is often thickened.

Stem 5–15 cm tall, 2–6 cm thick. Thicker near the top; toward the base it sometimes tapers or has a cone-shaped "appendage" (hence appendiculatus). Yellow in color, with a barely visible fine net in the upper part, sometimes with reddish-brown spots at the base.

The flesh is dense, juicy and white, and doesn't change color when cut or damaged — this feature sets porcini apart from a number of poisonous lookalikes. In old fruiting bodies the flesh becomes spongy and yellowish.

The taste is mild, nutty and slightly sweet. The stem flesh is denser and more fibrous than the cap flesh.

The flesh is buttery yellow, very firm in young mushrooms, softer in mature ones. When cut it may slowly turn blue, especially in the tubes and the upper part of the stem. At the stem base it sometimes has a pink or reddish-brown tint.

The smell is pleasant, unobtrusive, mushroomy with light nutty notes. With cooking and drying the aroma intensifies and takes on a deep, rich woody, foresty character. It's for dried porcini that the mushroom is so valued in cooking — no other dried mushroom gives such a pronounced taste and smell.

The smell is pleasant, mushroomy-nutty, with a faint note of fresh forest berries. The taste is mild and earthy, with no bitterness — some sources describe it as "buttery nuttiness".