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, add water equal to M divided by (1 minus M) times the total dry weight. At 60% moisture that is 1.5 times the dry weight in water, so the hydrated substrate weighs about 2.5 times its dry weight.

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.

Mushroom Substrate Recipe Calculator (Masters Mix) — sawdust, soy hull, bran, gypsum & water

Recipe preset

1 Batch size

How big is this mix?

Number of blocks / bags In this batch.

Dry base mix per block Sawdust + soy hull, before bran/gypsum & water.

2 Recipe

Sawdust + soy hull make up the dry base (should total 100%). Bran and gypsum are added on top of the base.

Hardwood sawdust % of base

Soy hull pellets % of base

Bran (wheat/oat) % on top Supplementation; skip if using soy hull.

Gypsum % on top ~1% typical · buffers pH, reduces clumping.

Target moisture % (field capacity) ~58–62% for most gourmet substrates. Squeeze test: damp, a drop or two, never streaming.

Shopping list & mix

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Total dry

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Water to add

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Hydrated total

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Hydrated / block

IngredientPer blockWhole batch

Dialing in a recipe block by block? Mycro logs each batch's substrate, spawn, and final yield — so you learn which mix actually gives your farm the best biological efficiency and lowest cost per pound, instead of guessing. Join the early-access list:

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

To hit a target moisture content M, water added = M ÷ (1 − M) × total dry weight. At 60% moisture that's 1.5× the dry weight in water, so a hydrated block ends around 2.5× its dry weight. "Field capacity" means fully hydrated but not dripping when squeezed firmly — a drop or two at most.

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)

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.

Next step: not sure if your mix is wet enough? The field-capacity guide shows the squeeze test and how to fix a batch that's too wet or too dry. Once it's mixed, the Grow Calculator estimates your spawn, expected yield, and profit per block — and the biological efficiency guide explains how to turn that substrate into the most mushrooms.