BSF metrics #4: substrate temperature

01 · The asymmetry

Temperature and humidity move differently

Moisture and temperature together decide whether your cycle hits 8 (even 6) days or stalls at 14.

Both have to be looked at from the substrate's and the larvae's point of view. Air is just the medium — what you use to keep substrate steady.

But the two work asymmetrically across the cycle.

Humidity stays constant. Temperature has to change.

02 · Humidity

Humidity holds the line

Air at min ~70% RH every day of the cycle. That's the floor that stops substrate drying throughout the process. The substrate dries on its own — larvae eat wet substrate and excrete dry frass. Air just has to hold the line.

03 · Temperature

Substrate is the target, air is the medium

Temperature is different. Substrate target is ≈30°C across the cycle, but the physics moving substrate temperature changes:

Early. Substrate is wet. It self-cools by evaporation, 4–5°C. Air must run hot — ~34°C — to land substrate at 30°C.

Late. Substrate has dried. Larvae are dense and active, generating significant metabolic heat from inside. Tray temperature climbs toward 40°C. Now air must run cool to absorb that heat.

04 · The bottleneck

Ventilation matters more than cooling

And here the bottleneck shifts. Ventilation matters more than cooling at the end.

Late cycle, the room doesn't need to be made cold. Heat has to be moved off the trays. That's airflow, not refrigeration.

05 · The trap

Removing heat without dropping below 70% RH

The trap: cooling dries air. If you run AC hard to drop temperature, RH falls with it — and the substrate surface starts drying before harvest. The engineering challenge of climate control isn't temperature and humidity in isolation. It's removing heat without dropping below 70% RH.

That's what dynamic climate control actually buys you.

06 · The floor

The cold-night profit killer

Below 25°C substrate or 50% RH, you're almost halted.

This is the cold-night profit killer. If overnight air drops to 20°C, substrate follows with a lag, especially in an outdoor setup. Larvae barely metabolise for 6–8 hours every night. Cycle stretches by 2–3 days. Margins gone before harvest.

07 · The trade-off

Pick one, but pick consciously

The trade-off you actually face.

Either tight climate control — within a few degrees of 30°C and at ~70% RH every batch — or roughly 70% of maximum performance, longer default cycles, margin compression. Pick one, but pick consciously.

08 · The baseline

Doing nothing has a cost

Even in tropical climates, batch-to-batch unpredictability without active management is the baseline. Simple greenhouse setups maintaining ~28°C have earned +40% larval yield over open-air in field conditions. Doing nothing has a cost.

09 · The margin

A tight margin business

BSF production is a tight margin business where all optimisations need to be considered and constantly improved. You cannot afford to leave 20% potential efficiency on the table from any part of the process. Unfortunately without any kind of climate mitigation, this is inevitable.

10 · The precondition

Stable conditions are the precondition

Do you want to build a BSF operation that's profitable and scales? Keeping substrate temperature steady — within a few degrees of 30°C, every batch, every cycle — isn't a luxury. It's the precondition. No progress, no learnings, no improvement without stable repeatable conditions.

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BSF Metrics #4 — Temperature: Substrate Is the Target, Air Is the Medium