Fully colonized rye grain spawn jar showing dense white mushroom mycelium growth What grain spawn actually is, why it outperforms spore inoculation, and how to prepare it correctly — including the sterilization and hydration steps where most growers go wrong. This article is part of the Spores Lab Substrate Preparation pillar. For the complete overview of substrate types, preparation methods, and sterilization principles, start at sporeslab.io/post/substrate-preparation-the-f