Biological efficiency, explained

What biological efficiency actually measures

Biological efficiency (BE) is the fresh weight of mushrooms you harvest divided by the dry weight of the substrate you grew them on, written as a percentage:

The "fresh vs. dry" part trips people up, so it's worth saying plainly: you weigh the mushrooms fresh, the moment you pick them, and you weigh the substrate dry — before you ever added water. A BE of 100% means one pound of fresh mushrooms for every pound of dry substrate. Because fresh mushrooms are ~90% water and dry substrate is, well, dry, a BE well above 100% is entirely possible and not a mistake.

BE is the great equalizer. A 5 lb block and a 50 lb bulk bed can't be compared by raw yield, but they can be compared by BE. It tells you how hard your substrate is working, independent of batch size — which is exactly why it's the number serious growers track strain by strain.

A worked example

You make a 5 lb (dry) Masters Mix block. Over three flushes it gives you:

BE = 4.2 ÷ 5 × 100% = 84%. Note that you count every flush, not just the first. Stopping the math at flush one is the most common way growers undercount their true BE — and then wrongly conclude a strain is underperforming.

What's a "good" BE?

It depends heavily on species, strain, substrate, and how well your conditions are dialed in. As rough, real-world targets across all flushes:

Chasing a record BE isn't always the right call. A slightly lower BE with near-zero contamination and a fast turnaround often makes more money than a heroic BE on blocks that take forever or get contaminated. BE is one input to profitability — not the goal itself.

Why BE drives your profit

Your cost per block is roughly fixed — substrate, spawn, bag, labor, energy. BE decides how many pounds that fixed cost is spread across. Push BE from 60% to 90% on a 5 lb block and you've gone from 3.0 lb to 4.5 lb of saleable mushrooms for the same inputs — that's a 50% jump in revenue per block and a big drop in your cost per pound. That single ratio is usually the difference between a farm that pencils out and one that doesn't.

Seven ways to improve biological efficiency

1. Supplement the substrate. Adding nitrogen — soy hull pellets, or 10–20% wheat/oat bran — is the biggest single lever for most wood-loving species. The Substrate Recipe Calculator scales a supplemented mix for you.
2. Sterilize properly when you supplement. Supplementation raises yield and contamination risk. The two go together: more nutrition feeds your mushroom and any mold that gets in. Clean technique is what lets you cash in the higher BE.
3. Hit field capacity, not soaking wet. Too dry starves the flush; waterlogged substrate goes anaerobic and stalls. Aim for ~60% moisture — damp, a drop or two when squeezed, never streaming.
4. Use enough spawn. A 20–30% spawn rate colonizes faster, crowds out contaminants, and often lifts total yield versus a thin 10% rate — see the spawn ratio guide.
5. Get fresh air and humidity right in fruiting. High CO₂ gives long stems and small caps; low humidity aborts pins. Lion's mane and others are especially fussy here — small improvements in your fruiting environment show up directly in BE.
6. Harvest and care for later flushes. Pick at the right moment, keep blocks hydrated between flushes, and you'll capture the second and third flushes that many growers leave on the table.
7. Match strain to substrate. Genetics matter. A vigorous commercial strain on the substrate it likes will out-yield a tired culture on a mismatched mix, every time.

Measure it, don't guess it

Every "typical" number on this page is a starting point. The BE that matters is the one your farm gets, on your strains and substrate, in your room — and the only way to know it is to weigh each batch and keep score over time. Growers who log it spot the strain that quietly underperforms for three cycles, the substrate tweak that added 15%, and the room that always lags.

General guidance from common cultivation practice, not guarantees — your results vary with strain, substrate, supplementation, and conditions. Mycro is for legal culinary & medicinal mushrooms only.