Though white button mushrooms are the most common at the local grocery store, they are among the hardest to grow. But Prairie mushrooms has the technique perfected and has been supplying mushrooms to most of northern Alberta since 1963. The company is a family-owned business which currently employs about 80 staff.
Nico Molenkamp has been involved with the company since he was in his teens, and is currently the head mushroom grower at the facility. The company grows all its own white button and portobello mushrooms, and redistributes dried and shiitake mushrooms.
The current facility contains 23 mushroom barns, that have multiple beds all in different stages of the growing cycle, which takes about eight to nine weeks. Humidity levels are high throughout all the barns in order to prevent the beds from drying out. Rooms are climate controlled, and careful attention is paid to temperature, humidity and carbon dioxide levels.
The first stage of the process involves loading beds with compost. Molenkamp says the creation of the compost is crucial to good mushroom growth. The compost consists mainly of wet wheat straw mixed with a small amount of chicken manure. After the mixture has sat for about two weeks, soybean meal and gypsum are added to promote the composting process. The moisture content of the compost is about 74 per cent.
The compost is created weekly outside the building year-round. Once the compost is ready, workers begin a 10-day pasteurization process. This involves heating the beds and the surrounding air to kill harmful bacteria and encourage the growth of bacteria needed for mushrooms.
Molenkamp said moisture and nitrogen levels are important factors for the best mushroom growth, and to create less competition from potential diseases and other fungi. After pasteurization, beds are cooled and root cuttings are mixed into the compost. The root cuttings are bits of mycelium spawned on rye, which are then left to grow for about seven days. Using root cuttings allows for consistency and reduces the possibility of genetic variation in the mushrooms. “During that time, we want to maintain the temperature in the bed at about 26-27 degrees Celsius,” said Molenkamp. “When you put the seed in, the moisture content is at about 70 per cent.”
Controlling the medium
In the next stage, a two-inch layer of a mixture of peat moss and lime is applied to the beds. The lime helps control the pH in the beds and traps water to make it available for the growing fungi. The peat is vital for button mushrooms, as they need a form of dirt in order to grow. The peat is watered for the next five to six days of the growing cycle.
In order to cause the mushrooms to form, the whole mixture needs to be cooled through a process known as flushing. The flushing cools the beds, introduces fresh air into the mixture and shocks the mycelium into bonding together into pins. These pins grow quickly as mushrooms can double in size each day.
The first crop is harvested after four days. Temperatures are reduced to about 15 degrees Celsius for cropping with humidity levels of about 80 per cent. Mushroom pickers monitor the beds and pick according to size and hardness. Many of the harvesters are so quick that they can pick up to 100 pounds of mushrooms an hour.
The mushrooms are sorted, and packaged right on site. In addition to the white button mushrooms, Prairie Mushrooms grows brown button mushrooms and portabello mushrooms.
Once the crop is harvested from a bed, it is heated and watered in order to generate another crop. Each bed generates three crops before it is killed off. The beds are cleaned and disinfected and the process is repeated. Spent compost is available to consumers who can purchase it for garden mulch.