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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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