Grain spawn is a type of mushroom spawn consisting of fungal mycelium colonizing sterilized grains, typically wheat, rye, or millet. It serves as the primary inoculant for mushroom cultivation, providing a nutrient-rich substrate for mushroom mycelium to grow and proliferate. Grain spawn is commonly used in various cultivation methods, including indoor and outdoor mushroom cultivation, and is available in different formats, such as jars, bags, or trays. With its versatility and effectiveness, grain spawn is an essential component for initiating the mushroom growing process and obtaining high yields of edible or medicinal mushrooms.