Process — How mushrooms are grown commercially

The diagram shows the eight stages in the commercial production of mushrooms.

Overall, mushrooms are farmed quite unlike ordinary crops: the entire process happens indoors in dark rooms, the growing medium is heat-treated compost rather than soil, and the crop is picked repeatedly in flushes instead of in one harvest.

Preparation comes first. Compost is mixed from straw and manure and left to heat naturally, after which it is pasteurised at 60 degrees to kill any pests and weeds. Once cooled, mushroom spawn is mixed evenly through the compost, which is then loaded into trays and stacked in dark, climate-controlled growing rooms.

The growing phase depends on precise conditions. Each tray is topped with a thin layer of peat known as casing, and the rooms are held at about 18 degrees. After roughly ten days, tiny pinheads appear on the surface, and these swell into full mushrooms which are picked by hand — with new flushes emerging every few days from the same trays. Finally, the picked mushrooms are chilled, packed into punnets, and delivered to shops within twenty-four hours, since freshness is everything in this trade.