Why manual checks miss the early stage
Spoilage starts as a localised pocket. Respiring grain, insects and mould all release heat and moisture, and because a grain mass is an excellent insulator, that heat stays concentrated instead of dissipating. By the time a hot spot is warm enough to notice from the surface or from a single probe sample, the affected volume has usually grown well past the point where aeration alone will fix it.
Post-harvest losses in developing regions are commonly estimated at 10-20% of cereal production by the FAO, with storage a significant share of that. The measurable part of the problem — temperature and moisture drift — is exactly what a sensor network is good at.
What gets measured, and where
A single reading at the top of a silo tells you about the headspace, not the grain. The useful signal comes from readings distributed through the mass.
| Measurement | Where it is taken | What it tells you |
|---|---|---|
| Grain temperature | Multiple depths on each probe cable | Hot-spot formation, insect activity, effectiveness of a cooling run |
| Interstitial humidity | Same depths as temperature | Equilibrium moisture of the grain at that point — the leading indicator of mould risk |
| Headspace temp / humidity | Above the grain surface | Condensation risk on the roof and upper layer |
| Ambient conditions | Outside the structure | Whether running aeration now would cool the grain or wet it |
| CO₂ (optional) | Headspace or exhaust | Rising respiration across the whole mass, often ahead of a temperature rise |
Safe ranges are grain-specific
There is no single safe number. Each grain has its own moisture ceiling for long-term storage, and every point of moisture above that ceiling shortens safe storage life sharply at warm temperatures.
| Grain | Target moisture | Target grain temp |
|---|---|---|
| Wheat | 12-13% | Below 15°C |
| Paddy rice | 12-14% | Below 15°C |
| Maize | 13-13.5% | Below 15°C |
| Barley | 12-13% | Below 15°C |
| Sorghum | 12-13% | Below 15°C |
The full breakdown, including aeration timing and the warning signs to look for, is in the grain storage guide.
From reading to action
Readings on their own are just a chart. The value is in what happens next:
- Baseline. Each batch gets its grain type, intake moisture and target thresholds recorded at fill.
- Trend detection. A point warming faster than its neighbours is flagged, not just a point crossing an absolute limit — drift matters more than a single number.
- Prediction. A model trained on storage histories scores each batch for spoilage risk so attention goes to the batch most likely to fail next, not the one that already failed.
- Alert and escalate. The technician on duty is notified first; unacknowledged alerts escalate to the warehouse manager.
- Act and record. Aeration runs, turning and inspections are logged against the batch, so the fix is auditable at sale time.
Frequently asked questions
What is grain storage monitoring?
Grain storage monitoring is the continuous measurement of temperature, moisture and humidity inside a stored grain mass, combined with a rule set that raises an alert when readings drift outside the safe range for that grain. Manual probing samples one point at one moment; continuous monitoring samples every depth on a fixed interval, which is what makes an early-stage hot spot visible.
How often should stored grain be checked?
Standard extension guidance is to inspect stored grain at least every two weeks in cool weather and weekly in warm weather. Sensor-based monitoring replaces that inspection interval with automatic readings, typically every 15 to 60 minutes, so the interval stops being the limiting factor.
What temperature rise indicates a problem?
A sustained rise at one probe point while neighbouring points stay flat is the classic hot-spot signature. A rise of roughly 2-5 degrees Celsius above the surrounding grain mass over a few days warrants investigation, because grain does not warm itself without biological activity — insects, mould or respiring high-moisture grain.
Does monitoring work without internet at the site?
Yes. GrainHero controllers buffer readings locally and forward them over LoRa to a gateway, then to the cloud when a connection is available. Readings taken during an outage are backfilled once the link returns, so the history has no gaps.
Can monitoring control aeration fans automatically?
Yes. Actuator control is rule-driven: fans can be triggered when ambient conditions are favourable for cooling or drying and blocked when running them would add moisture to the mass. Every automatic action is logged with the readings that triggered it.