Portobello mushrooms have a mild aroma similar to that of almonds. The stem yields to light pressure and the flesh turns light brown when a fresh cut is made. Portobello mushrooms thrive worldwide in fields and grassy areas and are harvested from June through October. They can be eaten raw but should not be confused with poisonous mushrooms like the deadly destroying angel (Amanita), Agaricus xanthodermus, or the Entoloma sinuatum.
From Wikipedia: “Agaricus bisporus is an edible basidiomycete mushroom native to grasslands in Europe and North America. It has two color states while immature—white and brown—both of which have various names. When mature, it is known as portobello mushroom, often shortened to just portobello (also spelled portabello or portabella). Smaller sized portobello mushrooms may be called portobellini or portabellini.
When immature and white, this mushroom may be known as common mushroom, button mushroom, white mushroom, cultivated mushroom, table mushroom, and champignon mushroom. When immature and brown, this mushroom may be known variously as Swiss brown mushroom, Roman brown mushroom, Italian brown, Italian mushroom, cremini or crimini mushroom, baby bella, brown cap mushroom, or chestnut mushroom.
A. bisporus is cultivated in more than seventy countries, and is one of the most commonly and widely consumed mushrooms in the world.”
Portobello mushrooms can be used like the smaller button or cremini mushrooms in cooking. They can be marinated and steamed, eaten raw in salads, and are often used as a hearty substitute for meat. Use a damp cloth or a soft mushroom brush to wipe each mushroom, one at a time, to remove any dirt. Mushrooms are very absorbent, so do not soak your mushrooms in water.
“The pileus or cap of the original wild species is a pale grey-brown in color, with broad, flat scales on a paler background and fading toward the margins. It is first hemispherical in shape before flattening out with maturity, and 5–10 centimetres (2–4 inches) in diameter. …The narrow, crowded gills are free and initially, pink, then red-brown and finally a dark brown with a whitish edge from the cheilocystidia. The cylindrical stipe is up to 6 cm (2 1⁄3 in) tall by 1–2 cm wide and bears a thick and narrow ring, which may be streaked on the upper side. The firm flesh is white, although stains a pale pinkish-red on bruising. ...This mushroom is commonly found worldwide in fields and grassy areas following rain, from late spring through to autumn, especially in association with manure. It is widely collected and eaten, even by those who would not normally experiment with mushroom hunting.”
“The common mushroom could be confused with young specimens of the deadly poisonous destroying angel (Amanita sp.), but the latter may be distinguished by their volva or cup at the base of the mushroom and pure white gills (as opposed to pinkish or brown of A. bisporus). Thus it is always important to clear away debris and examine the base of such similar mushrooms, as well as cutting open young specimens to check the gills. Furthermore, the destroying angel grows in mossy woods and lives symbiotically with spruce.
A more common and less dangerous mistake is to confuse A. bisporus with Agaricus xanthodermus, an inedible mushroom found worldwide in grassy areas. A. xanthodermus has an odor reminiscent of phenol; its flesh turns yellow when bruised. This fungus causes nausea and vomiting in some people.
The poisonous European species Entoloma sinuatum has a passing resemblance as well, but has yellowish gills, turning pink, and it lacks a ring.”
“…Originally, cultivation was unreliable as mushroom growers would watch for good flushes of mushrooms in fields before digging up the mycelium and replanting them in beds of composted manure or inoculating 'bricks' of compressed litter, loam, and manure. "Spore" collected this way contained pathogens and crops commonly would be infected or not grow at all. In 1893, sterilized, or pure culture, "spore" was discovered and produced by the Pasteur Institute in Paris, for cultivation on composted horse manure.
Today's commercial variety of the common mushroom originally was a light brown color. In 1926, a Pennsylvania mushroom farmer found a clump of common mushrooms with white caps in his mushroom bed. As with the reception of white bread, it was seen as a more attractive food item and became very popular. Similar to the commercial development history of the navel orange and Red Delicious apple, cultures were grown from the mutant individuals, and most of the cream-colored store mushrooms marketed today are products of this 1926 chance natural mutation.
A. bisporus is now cultivated in at least seventy countries throughout the world. Global production in the early 1990s was reported to be more than 1.5 million tons, worth more than US$2 billion.”
“Mushrooms contain hydrazine derivatives, including agaritine and gyromitrin, that have been evaluated for carcinogenic activity. Agaritine, a hydrazine, poses no toxicological risk to humans when mushrooms are consumed in typical amounts.”