Detailed Guide to Preparing Wheat Grain Substrate
Formula and treatment: 100 kg wheat grain, 10-20 kg dried stored fermented manure-straw or rice husk. 1-2 kg calcium carbonate or gypsum powder.
Wheat grain is rich in nutrients and promotes vigorous mycelial growth. To prevent premature decline of mycelial vigor, add 50 g magnesium sulfate and 100 g monopotassium phosphate per 100 kg wheat grain for better results. Choose wheat grains that are plump with thick hulls and free of insect damage or broken grains. Generally, aged wheat that has undergone a dormancy period gives better soaking results, absorbing water and softening quickly.
Soak the wheat grains in 1%-2% lime water, with the water level 10-15 cm above the grains. Stir frequently and remove floating grains. Adjust the soaking time flexibly according to water temperature. Soak until the interior of the grains has no white core left. Generally, at a water temperature of about 26°C, soaking takes about 12-14 hours. Remove the soaked grains, drain the water, and spread them on a clean cement surface to air-dry. Once the surface moisture of the grains has dried appropriately, mix in pre-moistened manure-straw filler, gypsum powder, etc. The standard for controlling water absorption by wheat grains when filling into spawn bottles is: after soaking and air-drying, every 100 kg of wheat grain should reach a wet weight of 136-140 kg.
Alternatively, soak the wheat grains in clean water for about 8 hours, then transfer to boiling water and boil for 15-20 minutes. When the grains are cooked through (no white core) but not broken or mushy, remove, drain, and spread to air-dry. When the surface moisture has dried appropriately, mix the ingredients as described above. This method allows the grains to absorb water evenly, which is beneficial for mycelial growth.
After absorbing water and adjusting moisture, the water content of the wheat grains must be appropriate. If the water content is too low, the grains are hard, mycelium penetrates poorly and sparsely, reproduction is reduced, and contamination is likely after inoculation. If the water content is too high, the grains become soft and spongy, easily burst during sterilization, starch leaks out forming a paste, grains tend to clump together, and after mycelial spread, a mycelial mat phenomenon may occur. In addition, the water content of the filler after pre-moistening should be close to that of the wheat grains.
Filler, also called sealing material, guiding material, bridging material, etc. It can fix the grain substrate and reduce the gaps between grains, thereby facilitating spawn block colonization and covering, promoting uniform mycelial spread, and avoiding mycelial breakage or mycelial mat formation caused by loose grains. Commonly used fillers include manure-straw, soil, rice bran, rice husk, etc. The filler accounts for about 10%-20% of the grain substrate. Generally, it should be relatively fine and short, preferably fermented after grinding. When mixing, the moisture content after moistening should be relatively consistent with that of the grains. The fermented dried stored filler must not be moldy. Materials that are too long or too coarse need to be crushed. Manure-straw should be pre-moistened with lime water about 4 hours before air-drying the wheat grains, at about pH 8. The water content should be 55%. Use half of the pre-moistened manure-straw as filler, mix thoroughly with wheat grains, gypsum powder, etc., then fill into bottles, and use the other half of the manure-straw as surface sealing material for the substrate.
When filling the wheat grain substrate, shake up and down to help the substrate bind relatively tightly. After filling, there is no need to punch holes, and conventional sterilization can be carried out. After cooling, inoculate with spawn. This method saves labor and is convenient, and is commonly used in large-scale production of wheat grain substrate.
Sterilization time: The wheat grain structure is compact and heat penetration is slow, so sterilization time needs to be longer. High-pressure sterilization gives relatively ideal results. Typically, maintain at 1.5 kg pressure for more than 3 hours, or at 100°C under normal pressure for more than 10-12 hours.