| Mushroom growing
is one of the most unusual stories in agriculture. Here is a summary of
how the most popular varieties are cultivated.
White mushrooms, like all mushrooms, grow from microscopic spores, not
seeds. A mature mushroom
will drop as many as 16 billion spores. Spores must be collected in the
nearly sterile environment of a laboratory and then used to inoculate
grains or seeds to produce a product called spawn (the mushroom farmer's
equivalent of seed).
Because mushrooms have no chlorophyll, they must get all their
nutrients from organic matter in their growing medium. The medium,
called substrate, is scientifically formulated of various materials such
as straw, corn cobs, cotton seed and cocoa seed hulls, gypsum and
nitrogen supplements. Preparing the substrate takes one to two weeks.
Then it's pasteurized and placed in large trays or beds. Next, the spawn
is worked into the substrate and the growing takes place in specially
constructed houses, where the farmers can regulate the crucial aspects
of heat and humidity.
In two to three weeks, the substrate becomes filled with the root
structure of the mushroom, a network of lacy white filaments called
mycelium. At that point, a layer of peat moss is spread over
the compost. The temperature of the compost and the humidity of the room
must be carefully controlled in order for the mycelium to develop fully.
Eventually, tiny white protrusions form on the mycelium and push up
through the peat moss. Farmers call this pinning. The pins continue to
grow, becoming the mushroom caps, which are actually the fruit of the
plant, just as a tomato is the fruit of a tomato plant. It takes 17 to
25 days to produce mature mushrooms after the peat moss is applied. Size
is no indication of maturity in mushrooms. Perfectly ripe ones vary from
small buttons to large caps.
Each crop is harvested over a period of several weeks and then the
house is emptied and steam-pasteurized before the process begins again.
The remaining substrate is recycled for potting soil. The harvested
mushrooms are set in carts, refrigerated and then packaged and shipped
quickly to supermarkets, food processors and restaurants. The entire
process from the time the farmer starts preparing the substrate until
the mushrooms are harvested and shipped to market takes about three months.
Crimini (Baby Portobello) mushrooms are grown and harvested in the same
manner as the white mushroom. The reason they have a darker color and
slightly denser texture is that they come from a different variety of spores.
Portobello Mushrooms
Portobello mushrooms are also grown like the white mushrooms. Actually,
the Portobello is a mature Crimini (Baby Portobello). It's usually three
to five days
older than the Crimini when harvested. As a result of their longer
growing period, Portobellos develop much larger caps-ranging up to six
inches in diameter.
Like other mushrooms, Oyster mushrooms are grown in mushroom houses but
they require a bit more humidity and fresh air than the white variety.
They grow well on a range of agricultural and wood waste products
including hardwood chips, chopped cereal straws or corn cobs. After the
growing medium is pasteurized and cooled it is inoculated, that is,
mixed with spawn and packed into long, tubular shaped plastic bags.
Holes are punched in the bags to allow the mycelia to breathe and the
bags are hung up or set on racks in the growing rooms. After about 14
days, the mushrooms pop out through the holes and can be harvested. If
straw is used as a growing medium, the substrate can be used as
fertilizer after mushroom production is completed.
Shiitake mushrooms were originally cultivated on natural oak logs, a
process which took two to four years before the mycelium colonized the
wood sufficiently to produce fruiting. Shiitakes were harvested on a
seasonal basis (spring and fall) over six years. Now, however, oak
sawdust is packed into poly bags, sterilized, inoculated with spawn and
placed in environmentally controlled rooms. These man-made "logs"
produce Shiitakes in seven weeks. The total process, from spawning to
the end of harvesting takes about four months as compared to the six
year cycle on natural logs.
For the Enoki, current technology uses automated systems to fill plastic
bottles with substrate usually ground corn cob pellets along with other
ingredients such as wheat bran and soybean meal. The bottles are
sterilized, inoculated with the mushroom culture and placed in growing
houses. When the substrate is fully colonized with mycelium, the bottles
are moved to an area where a plastic collar is attached to the mouth of
the bottle. This collar guides the forming mushrooms to grow straight up
to help control carbon dioxide. Enokis require a colder environment, 45
degrees compared to growing temperatures of about 60 degrees, which
other varieties require. After about 90 days, the mushrooms are
harvested. The collars are removed, the Enokis plucked from the mouth of
the bottle and usually packaged in shrink-wrapped bags. The remaining
substrate is recycled, since Enokis only produce one set of fruiting
bodies per crop. |
