Growing Mushrooms on Grain
By Marc-Andrew Donsky
e-mail: mad@amigo.net
Cultivation II
For growing mycelium for spawn production and/or
fruiting many types of grain can be used; rice, rye,
milo, wheat, rye grass seed. One spawn recipe uses bran
and perlite as a base. Again, many types of bran are
acceptable. Rye grain is one the most preferred grains
for spawn production because it does not tend to cake
together as easily as does rice or wheat berries. It is
also one of the least expensive grains and is quite
suitable to mycelial growth. Rice tends to form solid
cakes when sterilized. These "patties" are
excellent as fruiting tests for many varieties of
mushrooms. Caking can be avoided to some degree by the
addition of gypsum (calcium sulfate) (1-4 grams per
1/2-3/4 cup of grain) to the rice prior to sterilization.
Another method used to avoid caking is to precook the
grain, mix in the gypsum and then sterilize the blend.
The optimum moisture content for spawn grain is
between 49-54% (not counting the water in the uncooked
grain). For example, with rye grain use1 cup of grain
plus 3/4 cup of water (236 ml/cup) are placed into a
one-quart jar. The lids are loosely placed on the jars
and the filled jars are sterilized at 15 psi in a
pressure cooker for 45-120 minutes. It is important when
using standard Mason jar lids to invert the inner dome so
that the lid does not seal when the jars cool. Sealed
lids cause the inhalation of ambient contaminants upon
opening.
Calcium carbonate (chalk) can be added as buffer in
the amount of one to three grams per jar, but its use is
optional. Stamets recommends the addition of 1% (w/w) of
a 1:4 chalk/gypsum combination. That is one gram of the
chalk/gypsum to one hundred grams dry grain. When using
these calcium buffers the volume of water should be
increased by 10%. Stamets also advises soaking the grain
for 12-24 hours prior to heat sterilization. This initial
wetting will germinate heat resistant endospores. 4-10
hours soaking should be adequate. With healthy grain, the
seeds will begin to sprout in 12-24 hours.
After the jars of grain have been sterilized, they are
allowed to cool. They can then be inoculated with pieces
of mycelium overgrown agar or with portions of sterile
grain or sterile sawdust grown spawn. Immediately after
inoculation, the jars are shaken to spread the mycelium
throughout the grain. The jars are then stored in the
appropriate environment (humidity, temperature) with the
lids loose, to permit the exchange of gases. After 5-6
days, if growth seems slow or restricted to certain areas
of the jars, the jars are again shaken to disperse the
cells. Sometimes a third shake after 5 more days is
required to ensure a saturated growth. Once the grain is
saturated with pure mycelium it is ready to be used as
inoculum for more grain, compost or sawdust medium, or it
can be cased to induce fruiting.
Casing: The term casing refers to a
non-nutritive soil-like layer which is put on top of a
mycelium saturated grain or compost media. The casing
layer helps to induce fruit formation, support the
developing mushrooms and increase the fruiting yields.
The casing also provides the moisture essential to the
developing mushroom, and helps to maintain the
appropriate humidity. A typical casing recipe is: 1 part
peat 1 part vermiculite 1 part lime (calcium carbonate)
This mixture is moistened to 70% water content and is
then applied to the beds or jars to a depth of 1-2
inches. The casing is kept moist by light spraying, as
needed; taking care that water does not soak into the
mycelium below. We will discuss fruiting further in a
later column.
Next article: Compost Construction.
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