Agaricus bisporus

Agaricus bisporus, known as table mushroom, cultivated mushroom or button mushroom, is an edible basidiomycete fungus which naturally occurs in grasslands, fields and meadows across Europe and North America, though has spread much more widely and is one of the most widely cultivated mushrooms in the world. The original wild form bore a brownish cap and dark brown gills but more familiar is the current variant with a white form with white cap, stalk and flesh and brown gills.

Some grocery stores in the Western world sell this mushroom in canned and fresh preparations. An agaric, its gills are often left on in preparations. It can be found cooked on pizzas and casseroles, stuffed mushrooms, raw on salads, and in various forms in a variety of dishes. Mycologist Paul Stamets has raised concerns that this mushroom contains trace quantities of a chemical agaritine known to have carcinogenic properties, though whether levels are sufficient to cause harm in consumers is debated.

Taxonomy and naming
Agaricus bisporus is known by many names several of which refer to different stages; "button mushroom" when sold, collected or eaten in young, unopened form, "Crimini mushroom" or "baby bella" an immature portobello, or "Portobello mushroom" as a large brown mature mushroom. It is known as the champignon de Paris in France. It is also often called simply "champignon" (the french word for "fungus") in several languages.

The cultivated mushroom is a member of the large genus Agaricus, which has numerous members which are edible, tasty and collected worldwide. The next best-known is the commonly collected wild mushroom A. campestris, known in North America as the meadow mushroom or field mushroom in England and Australia. This can be found throughout much of the United States and Europe.

For many years it and other members of the genus were placed in the genus Psalliota.

Description
The pileus or cap of the original wild species is pale brown in color and 5-10 cm (2-4 in) in diameter; it is first hemispherical in shape before flattening out with maturity. The crowded gills are initially pink, then red-brown and finally a dark brown, as is the spore print. The stipe is up to 6 cm (2⅓ in) tall and bears a rough ring. The flesh is white though stains a pale pinkish-red on bruising.

Commonly found in fields and grassy areas after rain from late spring through to autumn worldwide, especially in association with manure. It is widely collected and eaten, even by those who would not normally experiment with mushrooming.

Similar species
The common mushroom can easily be confused with young specimens of the destroying angel (Amanita virosa), however the latter can be distinguished by their volva or cup at the base of the mushroom and pure white gills (as opposed to pinkish or brown of Agaricus bisporus). Thus it is important to always clear away debris and examine the base of a mushroom, as well as cutting open young specimens to check the gills. Furthermore, the destroying angel grows on mossy woods and lives symbiotically with spruce.

Culinary use
Common mushrooms are fairly rich in vitamins and minerals. The mushroom contains an especially high amount of vitamin B and potassium. Raw mushrooms are naturally cholesterol, fat, and sodium free. The mushrooms also have very low energy levels — five medium-sized common mushrooms added together only have 20 calories.

Common mushrooms have a unique flavor that can be matched by few other mushrooms. No specific flavor can be defined; most people describe the mushroom as "plain", but other people say that the common mushroom tastes slightly sweet or "meaty".

Like potatoes and apples, table mushrooms oxidize ("rust") quickly when exposed to air. When sliced and exposed to air for ten minutes or more, the mushrooms quickly soften, turn a brownish color, and lose their original flavor.

History of cultivation
The cultivated Agaricus bisporus common mushroom originated in France. Originally, cultivation was unreliable as mushroom growers would watch for good flushes of mushrooms in fields and then dig up the mycelium, replanting in beds of composted manure or inoculating 'bricks' of compressed litter, loam and manure. Spawn collected this way contained pathogens and crops would be commonly infected or not grow at all.

In 1893 sterilised, or pure culture, spawn was discovered and produced by the Pasteur Institute in Paris. Today's commercial variety of the common mushroom was originally a light brown color. In 1926, a Pennsylvanian mushroom farmer found a clump of common mushrooms with white caps in his mushroom bed. Like white bread it was seen as a more attractive food item and was very popular. As was done with the navel orange and Red Delicious apple, cultures were grown from the mutant individuals, and most of the cream-colored store mushrooms we see today are products of this chance natural mutation.

In most supermarkets, common mushrooms are marketed as "table mushrooms" and are often packed in small quantities. Mushrooms may be sold sliced or whole.

Portobello mushroom
The 'Portobello mushroom' is a large brown strain of the same fungus, left to mature and take on a broader, more open shape before picking. Portobello mushrooms are distinguished by their large size, thick cap and stem, and a distinctive musky smell. Because of their size and the thickness of their fleshy caps, these mushrooms can be cooked in a range of different ways, including grilling and frying.

Crimini mushroom
Although sometimes described a sub-variety of the portobello mushroom, the Crimini or Cremini mushroom is actually an immature portobello. Marketers have begun to refer to Crimini mushrooms as baby Portobellos and Portabellinis. Left to grow another 48 to 72 hours, a Crimini mushroom will more than quadruple in size, taking on the large-capped Portobello shape. They are more delicate in texture but still have the meaty Portobello flavor.

Agaritine
Common mushrooms, as all mushrooms of the genus Agaricus, have been found to contain very low levels of agaritine, which will metabolize into hydrazine, a well known carcinogen.

Cited texts



 * Kuo, M. (2004, January). Agaricus bisporus: The common mushroom Retrieved from the MushroomExpert.Com Web site: