Hot Spots in Stored Grain: How They Start and How to Catch Them

A hot spot is a pocket of grain that’s warmer than the grain around it — and getting warmer. Left alone, it can spread, cake, and downgrade a whole silo. Caught early, it’s usually a few hours of fan time or a turn of the grain.

How a hot spot starts

Almost every hot spot starts with one of two things: moisture or insects.

• Moisture. A damp load, rain through a leaking hatch, or condensation at the top surface gives moulds the water they need. Mould growth produces heat.
• Insects. Insect populations grow fastest in warm grain. Their activity produces heat and moisture, which makes the grain even more suitable for them.

Fines and broken grain make it worse. They collect under the fill point, pack tightly, resist airflow and hold moisture — the classic site for a core hot spot.

Why hot spots feed themselves

The biology runs in a loop:

1. Insects or moulds respire, producing heat and water.
2. Warmer, wetter grain lets them grow faster.
3. Faster growth produces more heat and water.

Because grain insulates so well, that heat doesn’t escape. Insect-driven hot spots commonly climb into the mid-30s °C; mould-driven heating in damp grain can go higher still. Moisture driven out of the hot core condenses in cooler grain nearby, starting the process in the next layer.

Signs to watch for

• A layer warming while others hold steady. The best early signal from temperature cables.
• Rising headspace CO₂. Respiration shows up as CO₂ before heat is obvious. See CO₂ in the Headspace.
• Moisture rising in one band. Often near the top, or above a warm core.
• Physical signs — crusting, a musty smell, condensation on the roof, insects on the surface. These are late signs.

What to do when you find one

1. Confirm it. Check the trend over a few days and compare layers.
2. Aerate on suitable air. Cool air through the grain slows insects and moulds and carries heat away. With a cooling fan, this may take many hours.
3. Core the silo. Drawing grain out of the centre removes the fines-rich core where many hot spots start.
4. Turn or move the grain if it’s badly affected, so you can break up the hot spot and inspect it.
5. Treat insects if they’re present, following label directions and safe fumigation practice.

Preventing them

• Store grain at or below safe moisture for the crop.
• Cool it quickly after harvest, then keep it cool.
• Keep hatches sealed and roofs sound.
• Core silos after filling to remove fines.
• Watch every level, every day.

How SiloSense helps

SiloSense IQ reads temperature and humidity at multiple levels down the silo every day, plus headspace CO₂, and the dashboard shows each layer’s trend. Alerts flag readings that need attention, so you can act while a hot spot is still small.

With Aeration Manager, you can start a Forced Run on the affected silo straight from the dashboard.

Request a demo to see it on your silos.