The Dirt on Mushrooms

The process of growing mushrooms has mystified people for years, leading to the misconception that mushrooms grow in straight manure. This belief has cause people to clean mushrooms in very unusual ways. From peeling to scrapping out the gills, people will try almost anything to get that dirt off the mushrooms.

Not very often is the question asked, what exactly are those specs of dirt on the mushrooms?

That dirt is most often sterilized peat moss. All Canadian mushroom growers use peat moss as the ‘casing layer’ on the top of the mushroom beds. Mushrooms are grown in beds in large growing rooms. The beds are made of wood, steel or aluminum. Before each crop is planted, the rooms and beds are sterilized at 160°F (71°C) for 24 hours, this ensures they will start with clean equipment.

The beds are then filled with a growth medium called substrate, which supplies carbon and nitrogen nutrients. The substrate is pasteurized at 136°F (58°C) for 8 hours before the mushroom ‘spawn’ are mixed into it. Spawn is mushroom mycelia attached to 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 what should you do to remove the specs of dirt? Simply give the mushrooms a quick rinse under cold running water and pat dry just before you enjoy them!

posted by Brittany