CO₂ in the Headspace: The Earliest Warning of Spoilage
Insects and moulds breathe out carbon dioxide long before grain heats or smells. Measuring CO₂ in the silo headspace can flag trouble days to weeks earlier.
SiloSense IQ ·
By the time stored grain smells musty, crusts over or feels warm, the damage is already done. The earliest sign of trouble is invisible: carbon dioxide.
Why CO₂ rises
Everything alive in a silo respires — it uses oxygen and gives off CO₂ and heat. In healthy, dry, cool grain that activity is very low. When insects multiply or moulds start growing, respiration jumps, and CO₂ builds up in the air between the kernels and in the headspace above the grain.
That rise usually comes before a temperature change you’d notice. Heat takes time to build to a level that shows up on a cable, especially if the hot spot is small and sits between sensors. CO₂ moves through the grain air and gathers in the headspace, so a single sensor at the top can pick up activity from a wide area below.
What the numbers look like
Outside air is roughly 400–450 parts per million (ppm) CO₂. As a rough guide for a sealed or closed silo headspace:
| CO₂ level | What it suggests |
|---|---|
| Near outside air (~400–600 ppm) | Grain is stable. |
| A sustained rise into the low thousands | Something is active — check it. |
| Several thousand ppm and climbing | Significant insect or mould activity likely. |
Exact thresholds depend on the silo, how well it’s sealed, the crop and whether fans have recently run, so the trend matters more than any single reading. A steady climb over days is the signal to look for.
Note that fumigation and aeration change headspace CO₂ too: fans flush it out, and some treatments raise it deliberately. Read CO₂ alongside what you’ve done to the silo.
Why it catches what temperature misses
- Small hot spots can sit between temperature sensors. CO₂ reaches the headspace regardless.
- Insect activity can be significant before it generates much heat.
- Early mould in a damp layer respires before the layer warms noticeably.
Temperature and moisture readings tell you where a problem is; CO₂ tells you that one is starting.
Acting on a CO₂ rise
- Confirm the trend over a few readings — not a one-off spike after a fan run.
- Check temperature and moisture at each level for a layer that’s warmer or wetter than the rest.
- Sample or inspect the grain.
- Aerate on suitable air, turn the grain, or treat as needed.
How SiloSense helps
SiloSense IQ includes a solar-powered headspace CO₂ sensor alongside temperature and humidity cables, with readings sent over LoRaWAN to the dashboard. You see the CO₂ trend for every silo, and alerts can flag readings that need a look — so you hear about trouble while it’s still small.
Request a demo to see CO₂ trends from a working site.