Moisture content plays a critical role in the successful colonization by mushroom mycelium of sterilized grai.:. If the grain is too dry. gro vth is retarded with the mycelium forming fine threads and growing slowly. Should too much water be added to the grain, the grain clumps, and dense, slow growth occurs. Higher moisture contents also encourage bacterial blooms. Without proper moisture content, spawn production is hampered, even though all other techniques may be perfect.
The optimum moisture for grain spawn falls within 45-55%, with an ideal around 50%. To determine the moisture content of any given formula, weigh 100 grams of the grain, dry it out, and re-weigh the remaining mass. (This can easily be determined by drying out the moistened grain in an oven for at 300° F. (150° C.) for 8 hours. The difference in weight is the water lost, or the percentage moisture.) Now water is xdded to achieve a targeted moisture content. Once cooked, a sample of grain is taken and oven dried. To check the proposed formula, just take the mass of the lost water divided by the total mass of dried grain and the lost water. This will give you a moisture percentage. Remember, moisture percentage is the mass of water divided by total mass, lost water included. This is not a ratio of water to dry mass, but a percentage of water over total mass. (This is a common mistake amongst certain schools of Shiitake growers and wood lot managers.) Once a targeted moisture content is achieved, spawn growers rely on volumetric scoops customized to the new formula for ease of handling.
Since grain comes to the consumer with an inherent moisture content of 8-15%, less water is added than might be expected to achieve the right moisture content for spawn production. Each cultivator may want to adjust the following proportions of water to grain to best fithis needs. Keep in mind that one liter (1000 ml.) of water weighs 1 kilogram (1000 g.) A quart is almost a liter and for the purposes of the mushroom cultivator can be used interchangeably. (The amount of grain within each vessel is specified in the following formulas .A variation of only 5-7 % between the two volumes is not statistically significant.) Gypsum is added to help keep the kernels separated after sterilization and to provide calcium and sulphur, basic elements promoting mushroom metabolism. (See Stoller, 1962; Leatham and Stahlman,1989.)
A delicate balance between the mass of grain and added water must be preserved to promote the highest quality spawn. As the spawn container is increased in volume, slightly less water
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