Mushroom Production
The general process for farming mushrooms involves six sequential steps, outlined below for the Agaricus species.
Mushroom Production
The general process for farming mushrooms involves six sequential steps, outlined below for the Agaricus species. The process is similar for other species, with the following slight process differences by species.
Oyster mushrooms are farmed by a similar process but require more humidity and fresh air and grow in tubular plastic bags rather than horizontal racks. Shiitake mushrooms are farmed using either natural oak logs or synthetic “logs” made from oak sawdust packed in poly bags. Enoki mushrooms are farmed in plastic bottles at colder temperatures (45°F) and only produce one set of fruiting bodies per crop. Beech mushrooms are farmed similarly to Enoki mushrooms but at higher temperatures (60-64°F). Maitake mushrooms are farmed on synthetic “logs”, similar to shiitake mushrooms, and only produce one set of fruiting bodies per crop.
Phase I Composting – Making the compost:
The first phase of composting begins by mixing and wetting the bulk compost ingredients on a large concrete slab called a wharf. Bulk compost ingredients may be natural (manure) or synthetic. Compost can include straw, peat moss, soybean or canola meal, chicken manure, horse bedding straw, grape must from wineries, potash, urea, ammonium nitrate, and/or lime. Nitrogen and gypsum supplements are added by topdressing the compost pile. A compost turner is used to mix and aerate the compost, and water is added as the bulk ingredients are mixed. The mixture is then stacked in piles with tight sides and loose centers, or ricks. Resulting conditions favor the growth of naturally occurring aerobic microorganisms, which produce heat through aerobic fermentation. Turning the hot (145°F – 175°F) compost pile regularly prevents conditions favoring the growth of anaerobes. Phase I composting usually occurs outdoors and takes 7-14 days to complete depending on the material used at the start.
Phase II Composting – Finishing the compost:
During this phase, which lasts 10-14 days, the compost is pasteurized to kill any pests present in the compost and remove ammonia formed during Phase I composting. High-temperature and low-temperature protocols are available. In the high-temperature protocol, the compost is heated to >145°F for 6 hours either through the naturally occurring heat produced by microorganisms or through added steam. After 6 hours, the temperature is lowered to 140°F, then the compost is allowed to cool at a rate of 2-3°F per day until the ammonia is dissipated. During the low-temperature protocol, the compost is heated to approximately 126°F using the same methods as in the high-temperature protocol, then the temperature is lowered by about 2°F a day for 4-5 days until the ammonia is dissipated. By the end of Phase II, the compost temperature must be lowered to 75 to 80°F before spawning can begin. Pasteurization is typically computer controlled, closely monitored, and well documented.
Spawning:
During this phase, the compost is inoculated with commercially produced mycelium (mushroom spawn) and held under controlled conditions to allow the spawn to colonize the substrate. The spawn will be evenly distributed throughout the compost while the compost temperature is held at 75°F and humidity is kept high, which allows the spawn to grow. This period, called the spawn run, generally takes 14-21 days.
Casing:
In this step, casing (a top-dressing of clay-loam field soil mixed with peat moss, ground limestone and, occasionally, spent, reclaimed mushroom substrate) is applied to the spawn-run compost and the crop is heavily watered. The casing acts as a water reservoir and is where thicker mycelia (called rhizomorphs) form. After casing, the compost is kept at approximately 75°F for 5 days with high relative humidity, then the temperature is lowered by 2°F per day until young mushrooms (pins) form. Although casing may be pasteurized either on farm or by commercial suppliers prior to receipt, recent research suggests that pasteurization of casing may not be beneficial as it may destroy microorganisms that competitively inhibit the growth of Listeria
Pinning:
When the rhizomorphs change from the vegetative growth stage to the fruiting growth stage, young mushrooms, called pins, push up through the casing layer. Pins develop in response to the introduction of fresh air into the growing room, which lowers the ambient concentration of carbon dioxide. The timing of fresh air introduction affects both yield and quality of the harvest and is best performed when the mycelium shows on the surface of the casing.
Cropping:
During this phase, mature mushrooms are harvested in 3-5-day periods called “breaks.” A complete harvest usually takes 30-42 days but can go on for up to 150 days. Air temperature during cropping is held between 57°F and 62°F to favor growth, however these temperatures may lengthen the life cycle of pathogens and pests.
Post-Harvest
Packaging methods for mushrooms can vary between farms, however fresh mushrooms should be refrigerated at 35° to 45°F. To limit spoilage and bacterial growth, mushrooms require a complete cold chain for storage and transport. Additionally, mushrooms should have adequate ventilation to prolong shelf life and should not be stored in unperforated plastic. Breathable pulp-trays are common for commercial mushrooms sales which allow for ventilation. When held within these conditions and packaged properly, the typically shelf life of mushrooms is 7-10 days.