Master's Mix Mushroom Substrate Calculator
Work out hardwood sawdust and soy hulls, plus water, for a batch of Master's Mix blocks — from the finished hydrated weight you want each block to be.
Learn the method behind this calculatorMaster's Mix here means equal dry masses of hardwood sawdust or pellets and soybean hulls or pellets — 50:50 of the dry solids, not 50:50 of the finished hydrated bag. Water is then added on top of those solids.
water = final mass × water% · dry solids = final mass × (1 − water%) · hardwood = soy hulls = dry solids ÷ 2
Between 45 and 75. Hydration depends on your pellet type, species and process — this is mass-balance maths, not a universal recipe.
Per block
Full batch — 10 blocks
Master's Mix Mushroom Substrate Calculator
- Blocks
- 10
- Water content
- 60%
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Worked example
10 blocks at 2.5 kg each is a 25 kg hydrated batch. At 60% final water content that is 15 kg of water (about 15 litres) and 10 kg of dry solids, split into 5 kg hardwood and 5 kg soy hulls. Per 2.5 kg block: 500 g hardwood, 500 g soy hulls and 1.5 kg water.
This tool does ingredient mass balance only. Different sawdust, pellets and soy hull products absorb and retain water differently, and some arrive with residual moisture, so treat the calculated water as a starting point and still check texture and field capacity by hand.
Supplemented substrate is nutrient-rich, which raises contamination risk. Cornell Small Farms describes supplemented sawdust and wood-pellet substrates as requiring sterilisation and clean, lab-style inoculation — do not inoculate this mix in an unclean workflow. No yield is guaranteed, and Master's Mix is not the right substrate for every species; shiitake and others often use different supplementation strategies.
Next steps
What this calculator does
Master's Mix is a supplemented substrate built from equal dry masses of hardwood sawdust or pellets and soybean hulls or pellets — a 50:50 split of the dry solids, not of the finished, hydrated bag. This calculator takes the number of blocks, your target hydrated weight per block, and your target water content, then works backwards to the water, hardwood and soy hull weights needed, per block and for the whole batch.
The maths is a straightforward mass balance: water is taken as a percentage of the finished mass, the remainder is dry solids, and those solids are split evenly between hardwood and soy hulls. It does not account for moisture already present in your ingredients, so treat the figures as a starting weigh-out, then adjust by feel.
When to use it
- Before mixing a batch of shiitake, lion's mane or oyster blocks on a hardwood-and-soy-hull recipe.
- When scaling a trial recipe (a single block) up to a full production run of ten, twenty or more.
- When comparing how a change in target water content shifts the water and dry-solid weights for the same block size.
- When ordering ingredients — the batch totals give a shopping-list weight for hardwood pellets and soy hulls.
Worked example
20 blocks at 2 kg each is a 40 kg hydrated batch. At 65% final water content that is 26 kg of water (about 26 litres) and 14 kg of dry solids, split into 7 kg hardwood and 7 kg soy hulls. Per 2 kg block that is 350 g hardwood, 350 g soy hulls and 1.3 kg water — the same ratios the calculator above shows for any block count you enter.
Common mistakes and assumptions
- Assuming 50:50 refers to the finished hydrated bag rather than the dry solids — it does not, and mixing this up changes every downstream figure.
- Ignoring residual moisture already in bagged hardwood pellets or soy hulls, which means less added water is actually needed in practice.
- Skipping sterilisation — Master's Mix is nutrient-rich and needs a clean, lab-style workflow, unlike straw pasteurisation for oysters.
- Using the same recipe for every species — shiitake, lion's mane and others often call for different supplementation strategies, not a one-size-fits-all mix.
- Not leaving headroom in the bag for gas exchange and expansion once the block is spawned.
FAQ
What ratio of hardwood to soy hulls does Master's Mix use?
The classic recipe is a 50:50 split by dry weight — equal parts hardwood sawdust or pellets and soybean hulls or pellets, before water is added.
What water content should I target for Master's Mix blocks?
This calculator accepts 45–75%, and many growers work somewhere around 55–65% of the final hydrated mass, but pellet type, particle size and your sterilisation method all shift what actually works. Always squeeze-test the mix before bagging.
Do I need to sterilise Master's Mix, or is pasteurising enough?
Supplemented sawdust substrates like Master's Mix are nutrient-dense and generally need sterilisation and clean inoculation technique, not just pasteurisation — see the Cornell Small Farms guidance linked below.
Which species is Master's Mix best suited to?
It is widely used for lion's mane and other gourmet species that respond well to supplemented hardwood. Shiitake growers often use a similar hardwood-and-bran approach but with different supplementation levels — check a species-specific recipe rather than assuming this one transfers directly.
Can I substitute other supplements for soy hulls?
Some growers use wheat bran or other supplements in place of, or alongside, soy hulls. This calculator's dry-solids split assumes soy hulls specifically; for a different supplement mix, use the water and total-solids figures and split the remainder yourself.
Related calculators and guides
- Substrate Hydration Calculator — generic water-to-add maths for any substrate.
- Grow Bag Calculator — scale a custom base/supplement recipe across a batch.
- Spawn Ratio Calculator — work out grain spawn once your blocks are mixed.
- Master's Mix substrate guide — the full recipe background and sterilisation notes.
- How to grow mushrooms at home (UK) — the full beginner walkthrough.
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