What exactly are those specs of dirt on fresh mushrooms?(NC) The specs of dirt that you occasionally see on fresh mushrooms are particles of peat moss. Most Canadian mushroom growers use peat moss as the 'casing soil' on top of the growing medium called substrate. The substrate supplies the nutrients to mushrooms. The peat moss holds the moisture. Mushrooms are grown in beds made of wood, steel, or aluminum. Before each crop is planted, the rooms are sterilized at 160°F (71°C) for 24 hours to ensure that the equipment is clean before each crop.
Then, the beds are filled with substrate that has been pasteurized at 136°F (58°C) for 8 hours, before the mushrooms seeds (or spawn) are mixed into it. Spawn is mushroom mycelia attached to a sterile grain, such as millet or rye. It is the seedstock of mushrooms. Spawn is delivered to the grower, in sealed bags from sterile laboratories that specialize in mushroom mycelia genetics.
In the beds, the substrate layer is about 8 inches (20 cm) thick. Two inches (5 cm) of peat moss is spread over the substrate to supply moisture. This is called the 'casing layer'. The mushroom mycelia permeate throughout the substrate and grow up through the casing layer. By controlling the temperature, humidity, oxygen and CO2, the grower stimulates the mycelia to form mushrooms on the surface of the peat moss. The whole process from spawning to harvest takes about 14 days.
So, the specs that you see on fresh mushrooms are “clean dirt.” There is no need to peel the mushrooms or scrape out the gills. Simply rinse the mushrooms under cold running water and pat dry just before you use them.More mushroom nutrition information and references, great tips and recipes can all be found online at www.mushrooms.ca.
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