1 Batch size
How big is this mix?
2 Recipe
Sawdust + soy hull make up the dry base (should total 100%). Bran and gypsum are added on top of the base.
Shopping list & mix
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How the recipe math works
No black box — here's exactly what the calculator does.
Base vs. additives
The base is your bulk carbon source, split between hardwood sawdust and soy hull pellets (they should add up to 100%). Bran and gypsum are then added on top of the base weight — so a 5 lb base with 20% bran and 1% gypsum becomes 6.05 lb of total dry ingredients before water. That matches how most growers describe and weigh a recipe.
Hydration to field capacity
The dry matter is what stays fixed, so a batch at moisture M weighs dry matter ÷ (1 − M), and the water to add is that total minus what you put on the scale. Bagged sawdust and soy hull pellets are not bone-dry — usually around 10% water — and that water counts. At 60% from 10%-moisture pellets it works out near 1.25× the weighed amount; from oven-dry material it is the familiar 1.5×. Ignoring the difference lands a batch nearer 64% than 60%, and too wet is the harder mistake to undo. "Field capacity" means fully hydrated but not dripping when squeezed firmly — a drop or two at most. More on field capacity.
Why these recipes
Masters Mix (50/50 hardwood sawdust and soy hull, ~1% gypsum) is the go-to for oyster, lion's mane, and many gourmet species — the soy hull supplies nitrogen so you skip separate bran. Supplemented sawdust (sawdust + ~10–20% wheat or oat bran) is the classic for shiitake and works well for many wood-lovers. Higher supplementation raises yield but also raises contamination risk if your sterilization isn't dialed in.
Common substrate recipes at a glance
| Recipe | Make-up (dry) | Good for |
|---|---|---|
| Masters Mix | 50% hardwood sawdust · 50% soy hull · ~1% gypsum | Oyster, lion's mane, most gourmet |
| Supplemented sawdust | Hardwood sawdust · 10–20% bran · ~1% gypsum | Shiitake, king oyster, wood-lovers |
| Soy hull only | 100% soy hull · ~1% gypsum | Cheap, fast oyster blocks |
| Straw pellets | 100% straw pellets | Oyster (low-cost, lower yield) |
Frequently asked questions
What is Masters Mix for mushrooms?
Masters Mix is a popular gourmet-mushroom substrate of 50% hardwood sawdust and 50% soy hull pellets by dry weight, usually with about 1% gypsum, hydrated to roughly 60% moisture (field capacity). The soy hull supplies the nitrogen supplementation, so no separate bran is needed.
How much water do I add to mushroom substrate?
To reach a target moisture content M, work from the dry matter rather than the bag weight. Sawdust and soy hull pellets are usually about 10% water as bought, so 10 lb of pellets is 9 lb of dry matter. The finished batch weighs that dry matter divided by (1 minus M), and the water you add is the difference between that total and what you weighed out. At 60% moisture from 10%-moisture pellets that is about 1.25 times the weighed amount; from genuinely bone-dry material it is 1.5 times, the figure the plain M divided by (1 minus M) formula gives.
How much gypsum should I add to mushroom substrate?
A common rate is about 1% of the dry substrate weight. Gypsum (calcium sulfate) adds calcium and sulfur, buffers pH, and reduces clumping so the substrate stays loose and well aerated.
Ranges are general guidance from common cultivation practice, not guarantees — your results vary with strain, supplementation, sterilization, and conditions. Always sterilize supplemented substrate properly. Mycro is for legal culinary & medicinal mushrooms only.