Substrate and Spawn Growth Management after Spawning

Substrate may lose about 5 F during spawning. During the summer, substrate may be warmer before spawn and therefore it is important to bring substrate temperature down to optimum temperature within 12-18 hrs after the spawning operation is completed. The mycelium within grain is slightly insulated; and this mycelium can survive in 90 F plus temperatures for a short time. However, with unfinished substrate it is usually better to be cooler than warmer when spawning, insuring the substrate temperature is brought down below the temperature range for mesophilic mold growth (> 85 F). The optimum spawn growth temperature is 75-76 F, however there is some indication that growth is faster at 73-75 F. Growers normally run substrate bed temperatures in the high 70's but most try not to exceed 80 F. At that temperature or higher the spawn growth becomes restricted and permanent damage to fruiting mechanism may occur. Spawn is killed at about 104 F.

Spawn growing temperatures should be maintained at a steady level. It is important to anticipate heat surges in substrate temperatures. Heat surges may occur early if the substrate is not conditioned properly. Spawn heat surges later in the growing period are a result of the spawn growth and dependent on the spawn and supplement type and rate. The initial first few days substrate activity should be minimal, unless substrate is unfinished and mesophilic microbes become active of the left over food. As tips of the spawn begin to contact each other and then fuse together (anastomose) more metabolic activity occurs. As the metabolic activity increases, more CO2, water vapor, other gases, and heat are produced. Gradually substrate temperature output will increase 6-9 days after spawning. Growers anticipate a heat surge at this time and will lower air temperatures before this heating occurs.

The removal of metabolic heat from the substrate involves conduction and other methods of heat transfer. Conduction is heat transfer by contact, like a touching a spoon in hot soup; eventually one feels the heat of the soup through the spoon. Metabolic heat is moves from one solid particle to another or water molecule to another. Therefore, tightly packed substrate with good moisture will help remove the heat from the substrate. Dense beds, less air spaces, its is easier for heat to be transfer to the surface and then removed. Loose, fluffy substrate is a harder to control more air spaces where heat transfer is slower. When the heat reaches the surface of the substrate heat it is removed by evaporative cooling and convection, heat transfer by circulation of currents from one region to another. Cooler air moving across the surface of the substrate removes the heat from the substrate. Evaporative cooling is the removal of heat when liquid phase turns to gas phase and occurs when dry air moves across the surface substrate moisture is lost and heat removed with it. Too much evaporative cooling is not good, since substrate will tend to dry out too much.