While considered fresh produce, mushrooms are neither fruit nor vegetable, but fungus. Mushrooms are extremely versatile and can serve as a tasty food source as well as a useful fertilizer for trees and soil.
Unlike most other produce, mushroom growth is actually hampered by sunlight. Instead, mushrooms feed on decaying organic matter and thrive in the dark.
Cultivated for centuries in China, there are more than 38,000 varieties of mushrooms (some highly toxic), with only about 300 edible species.
Before the advent of commercial agriculture, mushrooms were typically gathered in the wild and some varieties are still harvested this way.
Good quality, edible mushrooms can be difficult to grow; the cultivation process is not only labor intensive but highly sensitive to changes in the composting material.
Mushrooms are a staple in many international cuisines, particularly Asian dishes, which have been responsible for the worldwide popularity of shiitake mushrooms in particular.
The edible portion of a mushroom is the toadstool, which includes the stem and the cap. The wheel spoke-like underside of the cap contains the gills, which hold spores for reproduction.
Types & Varieties
Popular edible mushroom varieties include button, portabella, oyster, enoki, shiitake, crimini, lobster, porcini, and morels. Button mushrooms (Agaricus bisporus) are the most commonly grown in the United States. These are usually classified according to color: whites, creams, and browns.
Less than 15 mushroom types (including include button, shiitake, enoki, porcini, straw, oyster, common oyster, golden top oyster, phoenix tail, bear head, wood ear, hair wood ear, silver ear, and ling zhi) can be grown domestically due to the difficulty of cultivation. Pennsylvania leads the nation, producing two-thirds of U.S. production.
Morels, oysters, and chanterelles are often gathered in the wild, especially in the northeast and Pacific Northwest of the United States. Matsuke, white truffles, and black truffles are exclusively gathered from the wild as they need to interact with animals and trees in their natural environment to thrive.
Although cultivating mushrooms is complicated and labor intensive, crop lifecycles are a relatively brief 6 to 7 weeks (depending upon variety) and yields can be very high.
Commercial mushrooms are cultivated indoors in two stages: Stage 1 involves preparing the mushrooms’ food (nutrient-rich compost) and Stage 2 is the actual growing and harvesting of the mushrooms themselves.
In Stage 1, natural or synthetic compost is prepared (natural uses straw, hay, and manure) while synthetic can be made of corncobs, cottonseed hulls, corn stalks, dried grains, or cocoa bean hulls without manure.
Both kinds require the addition of nitrogen-rich supplements and moisture. Once the odor of ammonia disappears and the compost appears dark-brown, Stage 1 is complete. Heat is then used to pasteurize the material, killing off harmful microbes and insects.
Mushrooms thrive in cool, moist, well-ventilated environments. For Stage 2, compost is usually moved to slabs in a growing room.
Shiitake mushrooms grow on logs in the wild, but are cultivated commercially on synthetic logs made from sawdust, straw, corncobs, and other materials.
Temperatures must remain cool during cultivation, ranging from 50 to 75°F. Humidity should remain above 70% to prevent drying and splitting.
Growers spread mushroom spawn over the compost, then after 14 to 21 days soil is spread over the beds in a process known as casing. Beds must be watered regularly for about 3 to 4 weeks until the first mushrooms appear.
Pests & Diseases
With indoor growing the norm and pasteurization of the growing environment, pests are not a significant problem though various flies, gnats, mites, and millipedes, as well as nematodes will affect the growing process.
More common is postharvest damage from rough handling (causing bruises and discoloration) or improper cooling (leading to blackened stipes and gills and curled caps).
Although mushrooms are a form of fungus, they are still susceptible to a range of fungal, bacterial, and viral diseases including various mold, mildew, spot, and blotch outbreaks. Blotch and other bacterial diseases can lead to spoilage if not eliminated during growth and harvest.
Storage & Packaging
Harvested mushrooms need high relative humidity to prevent desiccation and loss of glossiness. Humidity between 95 to 98% is ideal.
Mushrooms are cooled to between 32 and 39°F, usually via rapid hydrocooling or forced-air and transported in refrigerated trucks immediately after harvest.
Properly cooled and packaged mushrooms can be stored for 7 to 9 days at between 32 to 34°F with 95% relative humidity. Even a small rise in storage temperature to 36°F shortens storage life by several days.
Mushrooms are susceptible to strong odors from items like onions in mixed loads, so they are generally packed and shipped in bulk cartons with a perforated overwrap to keep humidity in and odors out.
References: PennState Extension, UC Davis Postharvest Technology Center, University of Florida/IFAS Extension, University of Idaho, USDA, Western Growers Association.
GRADES & GOOD ARRIVAL
Grades consist of U.S. No. 1 and U.S. No. 2; quality defects include maturity, shape, stem length, diameter, open veils, and trim. Condition defects include firmness, discoloration, spots and decay, and exposed gills. Sizes run from small (three-quarters to 1.25 inches) to jumbo (3 or more inches).
Generally speaking, the percentage of defects shown on a timely government inspection certificate should not exceed the percentage of allowable defects, provided: (1) transportation conditions were normal; (2) the USDSA or CFIA inspection was timely; and (3) the entire lot was inspected.
|U.S. Grade Standards||Days Since Shipment||% of Defects Allowed||Optimum Transit Temp. (°F)|
There are no good arrival guidelines for this commodity specific to Canada; U.S. guidelines apply to shipments unless otherwise agreed by contract.
References: DRC, PACA, USDA.