Feature Friday: Mushroom Farming 101

One of the most common questions I encounter on a daily basis, besides how do you clean mushrooms, is “how do mushroom grow?”

There really is no simple way to answer this. The growing mushrooms contains a lot of steps, and a mushroom farmer must go through a very lengthy process before those white button mushroom you love and enjoy are shipped to your local market.

Let’s take a look a look at how mushrooms grow….

Contrary to popular belief mushrooms are not grown in manure. Mushrooms are in fact grown in a pasteurized substrate, which is made up of several different organic materials such as wheat, straw, hay, stable bedding, poultry litter, gypsum, corncobs, and high protein supplements such as soybean meal and feather meal. Each item does its job to create carbon & nitrogen, as well as manage the pH levels of the substrate. These items mixed together create a nutritionally balanced growth medium for mushrooms.

Pasteurization of the substrate is next. This is the most important step in making the substrate as it eliminates any pests or micro-organisms that may be in the mixture. During pasteurization the substrate reaches a temperature of 160F/71C, all bacteria is killed. The substrate is now ready for the spawn (fungal seed) to be added.

Mushrooms are “planted” using fungal mycelia instead of seeds. This “seed” or spawn is created in sterile, biosecure laboratories. Spawn making starts with a mixture of sterilized grain such as wheat, rye, or millet. Particles of mycelia are added to the sterilized grain and then incubated to promote the growth of spawn. Mushroom farmers then purchase this spawn mixture from the specialized commercial laboratories.

Mushroom spawn is then mixed thoroughly with the pasteurized substrate back at the farm. Temperature and humidity is then managed to promote the mycelial growth within the substrate. The mycelia (a mushrooms equivalent to a root) grows in all directions throughout the substrate from the spawn grain. After this spawning takes place the substrate and spawn mixture is transferred to several hundred beds or trays. A layer of casing is then spread over the mushroom bed. This casing is usually about 2 inches thick, and is made up of mostly peat moss. This casing layer acts as a water reservoir and provides a place where the mushroom mycelia form thick white rhizomorphs, which is what happens when mycelia grow together (it looks like white string). Because mushrooms need moisture, water is applied right after the casing. The beds are then watered periodically to the maximum holding capacity of the casing layer. In a few weeks the mushrooms will be ready for their first harvest.

Mushroom growers can often get more than one harvest from their single crop. Some can do two or three harvests with a 7 to 10 day break in between each harvest. The mushroom yield will decrease with each harvest of that single crop. Agaricus mushrooms are harvested for 16 to 35 days. During this harvest time bed temperatures, humidity and air ventilation are all controlled and monitored to ensure a healthy crop.

All mushrooms are hand harvested, which is very labour intensive work, believe me. After picking the mushroom from the bed the harvester then cuts off the base of the mushroom or the stump. The mushrooms are then immediately put into cold storage, this stops any mushroom deterioration or browning. This is also why you should keep your mushrooms in the fridge when you take them home. The mushrooms are then sent to packaging where they are either washed, sliced or cello wrapped in trays. Each package is weighed and then sent under a metal detector to make sure that no foreign objects were dropped into the container. They are now ready to be shipped.

The mushrooms that you see in your local grocery store were most likely picked 12-24 hours ago, so when you get them, you are getting the freshest mushrooms possible.

So there it is, the answer to every ones burning question, how mushrooms really grow. I hope this helps out all the people who have ever wondered.

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