Bulk Substrate Calculator

When to Use This Calculator

Use this calculator when filling grow bags for gourmet mushroom species like lion's mane, shiitake, oyster, or king oyster. It is especially useful when preparing Masters Mix (50/50 hardwood pellets and soy hull pellets), which is the industry standard substrate for most commercial gourmet operations. Whether you are making supplemented sawdust blocks, straw-based bags, or experimenting with different supplement ratios, this calculator ensures your ingredient weights and water volumes are precise every time.

Tips for Best Results

• •Always sterilize supplemented substrates at 15 PSI for at least 2.5 hours. Pasteurization alone is not sufficient when nutrients like bran or soy hulls are added — the extra nutrition feeds contaminants as readily as it feeds mycelium.
• •Higher supplementation rates produce higher yields but dramatically increase contamination risk. Start at 10-20% supplementation and only increase once your sterile technique is dialed in.
• •Let bags cool for at least 12 hours after sterilization before inoculating. Opening bags or adding spawn while they are still warm creates condensation that pools at the bottom and invites bacterial contamination.
• •Masters Mix (50% hardwood pellets, 50% soy hull pellets by dry weight) is the industry standard for most gourmet species. It provides an excellent balance of lignin, cellulose, and nitrogen for strong yields.
• •Always weigh your ingredients on a scale rather than measuring by volume. Pellets, sawdust, and supplements have very different bulk densities, and volume-based measurements lead to inconsistent ratios from batch to batch.