Moisture Migration: What Happens Inside a Silo Over Winter

You can put grain into a silo at a safe moisture, seal it, and still find a wet, crusted layer at the top in spring. No water got in. The moisture was already there — it just moved.

The convection current

Grain goes into storage warm, often at harvest temperatures in the 30s °C. As the weather cools, the grain near the walls and roof cools first. The core stays warm, because grain insulates so well.

That temperature difference sets up a slow air current inside the silo:

1. Air next to the cold walls cools, becomes denser and sinks down the outside of the grain.
2. It moves across the bottom and into the warm core, where it warms and picks up moisture.
3. The warm, moist air rises up through the centre of the silo.
4. At the top, it meets cold grain and a cold roof, cools, and drops its moisture.

Over weeks, that loop carries water from the warm core to the top centre of the silo. The average moisture of the silo hasn’t changed — but one layer has become a lot wetter.

Why the top layer spoils

Moisture deposited near the top surface raises the moisture of that grain, sometimes well above safe storage levels. Add condensation dripping from the roof and you get:

• crusting and caking at the surface;
• mould growth, sometimes visible as a grey or green layer;
• a starting point for heating and insect activity.

In summer the current can reverse, carrying moisture toward the bottom — but in Australia the winter pattern, after warm harvest grain, is the one that causes most trouble.

Stopping it: equalise the temperature

Moisture migration is driven by the temperature difference between the core and the outside of the grain. Remove that difference and the current stops.

That’s the main job of cooling aeration after harvest: move a cooling front right through the silo so the core is as cool as the edges. Once grain is uniformly cool, there’s very little to drive migration.

Practical steps:

• Aerate soon after harvest to pull field heat out of the core.
• Keep aerating on cool air until the cooling front has reached the top.
• Use ventilated or well-sealed roofs as designed, and check for condensation.
• Core the silo to remove the fines-rich centre, which resists airflow and stays warm.

Seeing it happen

Migration shows up in sensor data before you’d see it by eye:

• A warm core that isn’t cooling while the edges do.
• Rising humidity and moisture in the top sensor levels through autumn and winter.
• A gap between the bottom and top temperatures that won’t close.

How SiloSense helps

SiloSense IQ shows temperature, humidity and calculated moisture at each level of the silo, every day, so you can watch a cooling front move up and spot moisture building at the top.

Aeration Manager then runs fans on suitable air to close that temperature gap — in Automatic until the silo is cool through, then Auto Protect to keep it there.

Request a demo to see layer data from a silo through winter.