Creating Grain Spawn: A Beginner’s Guide to Scaling Up Mushroom Cultivation

Grain spawn is the backbone of larger mushroom cultivation projects. By creating your own grain spawn, you can propagate mycelium more efficiently and scale up your mushroom-growing efforts without breaking the bank. In this guide, we’ll take you through the complete process of preparing grain spawn, including selecting the best grains, the sterilization process, and proper inoculation techniques.

What is Grain Spawn and Why Use It?

Grain spawn is a grain-based substrate that has been inoculated with mushroom mycelium. It serves as a starting point for bulk cultivation, allowing mycelium to colonize efficiently before it is introduced to a larger substrate like straw, hardwood sawdust, or coco coir. Using grain spawn can increase the yield and vitality of your mushroom crop, as it offers a rich and nutritious base that accelerates growth.

Common Grains Used for Grain Spawn:

• Rye: Rye is widely considered the gold standard for mushroom spawn. It has an ideal balance of nutrition and moisture, and its size allows for even colonization.

• Wheat: Wheat berries are also a good option for grain spawn and are more accessible in some areas.

• Millet and Sorghum: Smaller grains like millet are excellent for spreading inoculum evenly throughout the substrate due to their large surface area.

Step-by-Step: Preparing Grain Spawn

1. Soak the Grains

   • Why Soak? Soaking grains for 24 hours allows them to hydrate fully and also helps to germinate bacterial endospores, which are then more easily destroyed during sterilization.

   • How to Do It: Measure the desired amount of grain (for beginners, start with 1 kg), and fill a large container with cold water. Add the grain and let it sit for 24 hours, stirring occasionally to ensure all the grains are submerged.

2. Boil the Grains

   • After soaking, boil the grains for about 10-15 minutes. The goal here is to bring the grains to field capacity, where they are plump and hydrated without bursting. Overcooking the grains can make them too mushy and more prone to contamination.

   • Drain the grains thoroughly using a colander and let them cool. Excess water must be drained completely to avoid anaerobic conditions in the jars.

3. Load the Jars

   • Once cooled, fill sterilized mason jars two-thirds full with the hydrated grain. This leaves space for shaking, which helps the mycelium spread during colonization.

   • Filter Lids: Cover the jars with modified lids that include a breathing filter. Use a piece of polyfill or micropore tape to allow gas exchange, while also blocking contaminants from entering.

4. Sterilize the Jars

   • Place the jars in a pressure cooker. Sterilize at 15 PSI for 90 minutes to ensure all bacterial spores are killed. Sterilization is crucial because grain is nutrient-rich and highly susceptible to contamination.

   • Let the jars cool completely before moving on to inoculation.

Inoculating the Grain Spawn

1. Clean Workspace: Set up a still air box (SAB) or work in as clean an environment as possible. Spray all surfaces with 70% isopropyl alcohol.

2. Inject with Liquid Culture or Spore Syringe: Using a sterilized syringe, inject 2-5 mL of liquid culture or spore solution into the jar. Aim to distribute the inoculum evenly throughout the jar.

3. Shake and Colonize: Shake the jar to distribute the inoculum. Place the jars in a warm, dark location at about 21-25°C for incubation. Within 1-2 weeks, you should see healthy mycelial growth.

Expanding Your Spawn for Bulk Substrates

Grain spawn can be used to inoculate a bulk substrate. Once your grains are fully colonized and have turned bright white with mycelium, they are ready to use. Here’s how:

1. Substrate Preparation:

   • Prepare a bulk substrate like pasteurized straw, hardwood sawdust, or coco coir.

   • Break up the fully colonized grain spawn and mix it thoroughly with the bulk substrate at a spawn-to-substrate ratio of 1:5.

2. Incubation and Fruiting:

   • Place the inoculated substrate in a bag or tray, and keep it in incubation conditions until fully colonized. After colonization, introduce fruiting conditions by providing light, fresh air exchange, and high humidity.

Conclusion: Why Make Your Own Grain Spawn?

Producing your own grain spawn allows you to scale up your mushroom cultivation affordably. It gives you control over the quality of your spawn, reduces costs, and enables you to expand exponentially from a single syringe of liquid culture. By learning to create grain spawn, you’ll be taking a significant step toward becoming a more self-sufficient and skilled mushroom cultivator.