Get the real “dirt” on fresh mushrooms

“Mushrooms are grown in pure manure!”

It’s a very common misconception, and I hear it almost every time I even mention mushrooms… I’m not going to lie, it sort-of drives me crazy… (Come on! They’re not grown in pure manure, I swear!!)

It is also this common misconception that leads people to clean mushrooms in very unusual ways…. Do we have any peelers in the house? How about gill scrappers? Or my favourite, soak ’em in water until they are soggy…?

Because people don’t know what the heck that dirt actually is, they will try almost anything to get it off. So let’s take a step back and examine what the real dirt on mushrooms is….

It is peat moss. Simple and straight forward – peat moss.

All Canadian mushroom farmers 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 farmer, 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? Let’s ask a Mushroom Farmer

Nick, how should you clean mushrooms?

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One comment

  • Suzie Ridler May 13, 2011   Reply →

    Great post! Although some people would disagree about running them under water. For me, if they're very fresh I can usually just brush the peat moss off using a paper towel but if they're older and it is holding on stubbornly, I will use water.

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