You actually know this mushroom very well. You buy it in 3 different stages of its growth. When very young, it’s sold as a “button mushroom.” When in “middle age”, it’s sold as Cremini / Crimini. When fully-grown, it’s sold as “portobello” (or some random spelling variation thereof.)
When harvested young, they are white, and have a very mild flavour. The older they get while growing, the darker they get in colour and the richer the flavour becomes.
Almost all other mushrooms need spore from another mushroom to pollinate them in order to produce a mushroom. Agaricus mushrooms don’t — which makes them easy to grow, but hard to do cross-breeding with.
As of 2004, 90% of all mushrooms in North America grown for market, and 95% of those in the UK, are Agaricus bisporus. In the rest of the world, however, they are less popular, so overall they only end up accounting for 40% of the world-wide market.
Agaricus can’t decompose material as other mushrooms can. It can only grow with material that has already been composted. The compost has to be made of material that other competing funguses don’t want to grow in. It’s usually made of straw and horse manure, but it can also be made of corn cobs, cotton seed hulls, dried brewers grain, hay, and poultry manure. The compost is sterilized with steam to kill the bacteria and fungus that did the breakdown of the materials to make it. It’s then “seeded” with Agaricus mushroom spawn. This spawn is mixed into the compost, where it begins to spread throughout the compost with weblike fungus growth on the surface within 2 to 3 weeks.
It is then covered with a layer 1 ½ to 2 inches deep (3.5 to 5 cm) of “top soil” if you will, which is a mixture of limestone and peat. In about 5 days, little mushrooms will start to poke through the top soil. Within about 2 weeks after that, the first crop of mushrooms will be ready to harvest. Between the harvesting of each crop, the farmer needs to allow 3 to 5 days for the next crop to be ready to harvest. Each crop is called a “flush.” Three to five crops can be picked, then after that the entire mushroom bed is discarded and a new batch is started from scratch.
Though there are several different species of Agaricus mushrooms, not all are friendly: those such as Agaricus xanthodermus (the “Yellow Staining Mushroom”) and Agaricus placomyces are poisonous.
There was some talk in the 1970s that a compound found in Agaricus Mushrooms, agaritine, could cause liver cancer if the mushrooms were eaten raw. (Medical Tribune, 27 April 1977). Shiitake mushrooms contain the same compound. You would have to eat 300g of these mushrooms all at once, and your body would have to convert all of the agaritine to diazonium derivative, which is very unlikely to happen. The lifetime cumulative risk of cancer has been estimated to be two cases per 100,000. Each 100g of Agaricus mushrooms contains about 300mg of agaritine, which is not destroyed by cooking.
The first known cultivation of Agaricus Mushrooms was in 1650 in Paris, France. They were grown in open fields until about 1800, when it was realized that this mushroom species required no light at all. Cultivation was then moved to caves or tunnels where the temperature and humidity could be more tightly controlled. Cultivation then spread to Britain, reaching America by 1865. Agaricus spawn was imported from Great Britain until the development of spawn in America in 1903.
In older books, when the study of mushrooms was still in its early days, all mushrooms with gills were classed as “Agaricus”.
Agaricus used to be known scientifically as Agaricus brunnescens, because it browns as it ages or when it is bruised. “Brunnescens” means browning. It’s similar to “brun” as in French for brown or “bruno” as in Italian for brown.