Week 3 Tutorial: Substrate in, substrate out

Week 3 tutorial — size a fruiting operation from the substrate you actually have, and account for the five kilograms that leave for every kilogram picked

11 March 2027

Time

90 minutes in the room, plus about 30 to tidy the output

Graded

Checkpoint 2 of 10, 2 % — a good-faith attempt at the output below

Due

5 pm, 12 March 2027

What this tutorial is for#

Two numbers come out of a fruiting operation, and most people write down only the first. Today you size both, and find out which one actually matters.

Story stage. Scoping. Quiz 1 runs first, so arrive on time.

Open these first#

• Your workbook, sheet 2 — week 2’s planting plan. Your prunings estimate comes off the planted area.
• Week 3’s lecture, for the biological efficiency ranges and the species temperature bands.
• The price schedule if you intend to cost a chamber.

If you missed week 2#

Use the labelled practice planting area and redo it on your own home later: PRACTICE — Wattle Street, 100 m² of back beds planted, producing roughly 60 kg of prunings and spent stems a year. Invented round numbers for teaching.

The words this week uses#

• Substrate — what the fungus eats. Straw, sawdust, prunings, or a supplemented mix. Measured dry.
• Biological efficiency (BE) — fresh mushroom mass ÷ dry substrate mass × 100 %. It can exceed 100 % because mushrooms are mostly water. It is not a thermodynamic efficiency, and comparing it to one is a category error.
• Spent substrate — what is left after fruiting. About five kilograms fresh for every kilogram picked, and the real output of the week.
• Fruiting months — the months your site’s mean temperature sits inside some available species’ band.

Do this#

1. Quiz 1 (20 minutes). On paper, on weeks 1 to 3. Five conceptual questions, no calculators.

2. Estimate the substrate you have (20 minutes). Prunings from your own planted area, plus a stated import. “Straw is cheap” is not a quantity — if you are importing, write down how many kilograms a year and price it from the schedule. A supply you did not derive from your own site is a supply you cannot defend.

3. Size the operation (25 minutes). Two outputs, not one:

The 20 kg is the lecture’s worked example at Brisbane. Use your own substrate estimate, and name the BE you picked and why — straw substrates run about 60 to 80 %, sawdust 13 to 61 %. These are the course’s least-verified figures, drawn from search summaries rather than papers read in full, and they carry a medium confidence label. Say so on your sheet.

4. Then the argument (20 minutes). Somebody in the room will want to feed spent substrate to the larvae, because every diagram online does. Work out together what 1.46 % bioconversion means for a 100 kg substrate stream, and where the arrow should go instead. It goes to compost and soil.

The output#

A substrate mass balance on its own sheet: dry substrate in, fresh mushrooms out, spent substrate out with its mass and destination, and the spent substrate’s nitrogen carried forward into your soil plan. Both arrows, or the balance does not close.

Check your own before you submit#

1. Is your substrate supply derived from your own site, with any import stated as a mass and a cost?
2. Is your BE inside the published range, and is the figure written down?
3. Is spent substrate on the sheet as an output, with a mass and a destination?
4. Is there an arrow from spent substrate to the insect unit? There should not be.
5. Are the fruiting months on your sheet, with the species band they come from?
6. Does the sheet say the yield figures carry a medium confidence label?

Where it goes next#

Spent substrate mass and its nitrogen carry into week 10’s compost balance. Write it down now; it is the stream most often lost between weeks.

Back to week 3 overview