Hermetic Storage

In a sealed store the biological activity of the contents changes the internal atmosphere. Insects and, to a lesser extent, grain and moulds use up oxygen through respiration and give off carbon dioxide. As oxygen becomes scarce and carbon dioxide accumulates, insects are stressed, stop developing, and eventually die, so populations decline rather than multiply. The effect is strongest when the grain is dry, because dryness limits the respiration of moulds that would otherwise raise moisture and heat.

The approach is sometimes described as biogenerated modified atmosphere, to distinguish it from controlled-atmosphere storage where gases are added and regulated by equipment. Its great practical advantage is simplicity: no gas cylinders, power, or specialist skills are required, only a container that stays sealed.

Multi-layer plastic bags

Grain is sealed inside one or more airtight plastic liners, often within an ordinary woven sack; low-cost and widely promoted for smallholder grain and seed.

Cocoons and flexible tanks

Large gas-tight fabric enclosures that hold bagged or bulk grain, used for community and commercial-scale storage.

Sealed metal and plastic silos

Rigid containers with airtight lids that store grain hermetically and also exclude rodents and re-wetting.

Hermetic systems are used for cereals, pulses, coffee, cocoa, and seed. For seed in particular, the low-oxygen, stable-moisture environment helps preserve germination as well as protect against insects.

• Dry grain to a safe, uniform moisture content before sealing — hermetic storage controls insects, not excess moisture.
• Fill and seal cleanly, removing residual insects, and keep the container closed as much as possible.
• Inspect bags and seals for punctures or leaks, which admit air and defeat the low-oxygen effect.
• Protect thin bags from rodents and sharp objects that can tear the airtight layer.