The denominator is dry substrate, and that is the whole point
Biological efficiency is defined as the fresh weight of mushrooms harvested divided by the dry weight of the substrate they came from, expressed as a percentage. Not the wet block. Not the block plus the bag. The bone-dry substrate.
BE = fresh mushroom weight ÷ dry substrate weight × 100
That definition is why BE can exceed 100 per cent without anything being wrong. Fresh mushrooms are mostly water; dry substrate has had its water taken out by definition. Comparing a wet thing to a dry thing gives a ratio bigger than one long before anything remarkable has happened.
The trouble starts when the same harvest is divided by the wet block weight instead. A 5 pound block at 60 per cent moisture holds 2 pounds of dry substrate. A pound and a half of mushrooms off it is 75 per cent BE against the dry weight and 30 per cent against the wet block. Both are real ratios. Only the first is biological efficiency, and the gap between them is one divided by the solids fraction — 2.5 at 60 per cent moisture, 2.86 at 65 per cent, 3.33 at 70 per cent, and about 5 at 80 per cent.
Two growers comparing notes, one quoting each way, will conclude that one of them is more than twice as good as the other. Neither number tells you that. The rule that avoids the whole mess is to write the substrate moisture down beside every BE figure you record.
Flushes are a distribution, not a prediction
A block does not give its whole yield at once. The page splits a total you already have across the flushes you count, using a ratio you supply, and reconciles the split to the pound so the lines add up to the total exactly rather than approximately.
What it will not do is tell you how a block behaves. Whether a second flush is half the first or two thirds of it, and whether a third is worth the shelf time it occupies, is a question for your own harvest records. The calculator has no opinion, supplies no figure, and does not know what you are growing.
| Substrate moisture | Dry substrate in a 5 lb block | 1.5 lb harvest, BE on dry | Same harvest on the wet block |
|---|---|---|---|
| 55% | 2.25 lb | 67% | 30% |
| 60% | 2.00 lb | 75% | 30% |
| 65% | 1.75 lb | 86% | 30% |
| 70% | 1.50 lb | 100% | 30% |
Read that table sideways. The harvest is identical in every row and the wet-block ratio never moves, while the BE swings from 67 to 100 purely on a moisture figure nobody wrote down. That is why a BE number without its moisture is not a measurement.
Fresh weight, dried weight, and what to sell
Fresh mushrooms are largely water, so the dried yield is small and the ratio is steep. At 90 per cent moisture, ten pounds of fresh gives one pound dried. At 92 per cent it takes twelve and a half pounds. Measuring it is the same low-oven exercise as everything else: weigh a tray, dry it to constant weight, weigh again.
Once you have the fresh weight, the dehydrator and freeze dryer tray load calculator works out the tray area, the runs and what the dried result fills. It handles the whole drying side, which is why nothing here does.
Where the inputs come from
The block weight and its moisture come from the substrate batch calculator, which also gives the per-block cost. The spawn rate calculator covers the spawn side, and the grow room staging calculator turns a weekly yield into the room space that holds it. For log-grown crops, the log inoculation calculator counts the holes rather than the blocks.
Questions people ask
Is biological efficiency measured against wet or dry substrate?
Dry. The definition is fresh mushroom weight divided by the dry weight of the substrate. A figure quoted against the wet block is a different ratio with the same name, and at 60 per cent substrate moisture the two are 2.5 times apart. At 80 per cent moisture they are about five times apart. Always record the substrate moisture beside the BE figure.
How can biological efficiency be over 100 per cent?
Because it compares a wet weight to a dry weight. Fresh mushrooms are mostly water and dry substrate is not, so the ratio passes 100 per cent without anything unusual having happened. It is not an efficiency in the thermodynamic sense and it is not bounded at one.
Does this calculator tell me what yield to expect?
No. It converts between a BE figure and a yield, in either direction, using numbers you supply. The efficiency itself comes from your own records or a cultivation reference, and the page supplies none and has no view on what is achievable with anything.
How should the flush split be set?
From your own harvest records. The page takes a ratio of each flush to the one before and divides the total by it, reconciled so the flushes add to the total exactly. Set it to 100 per cent for an even split. It distributes a total you already have; it does not predict one.
How much fresh weight makes a pound dried?
It follows directly from the fresh moisture. At 90 per cent moisture it takes ten pounds of fresh; at 92 per cent, twelve and a half. Weigh a tray, dry it to constant weight and weigh it again to get your own figure rather than using a general one.