Grain Storage Silo Problems

Grain is hygroscopic and continuously exchanges moisture with the surroundings. Ideal storage moisture is 12-14% for most grain types – above this level, biological activity accelerates which can lead to quality loss and health risks. The biological nature of grain means it breathes – it consumes oxygen and produces carbon dioxide, heat and moisture. This metabolic activity increases with temperature and moisture content, and can create self-reinforcing hotspots where temperature rises uncontrollably. Particle size variation in grain creates segregation during filling. Fine particles and dust collect in the centre of the silo, while coarse grains distribute towards the walls. This segregation creates zones with different permeability that affect airflow through the material mass.

Moisture-related problems are the biggest threat to grain quality during storage. Condensation on silo walls occurs when outdoor temperature drops and creates a moist layer between the grain and the silo wall. These are ideal conditions for mould growth. Aspergillus, Penicillium and Fusarium are the most common moulds in grain silos. Some of these produce mycotoxins – toxins that make the grain unsuitable as food or feed raw material. Aflatoxin from Aspergillus flavus is among the most dangerous known mycotoxins. Monitoring temperature and moisture in the grain mass is essential. Modern grain silos are equipped with temperature cables that measure temperature at various points through the material mass. A sudden temperature increase is an early warning sign of biological activity and potential mould growth.

Insects such as grain beetles, flour moths and grain moths can cause significant storage losses. They thrive in warm, moist environments and can reproduce rapidly if conditions permit. Insect activity generates additional heat and moisture, which worsens the problem. Prevention includes thorough cleaning of the silo between storage seasons, temperature control and good ventilation. Some facilities use controlled atmosphere – replacement of air with nitrogen or carbon dioxide – to kill insects without chemicals. Cleaning of the silo internal surfaces is critical for removing residues of old grain where insects can overwinter and establish populations. All cracks, corners and surfaces should be thoroughly cleaned between storage seasons.

Bridging and ratholing occur in grain silos, particularly with materials that have high moisture content or that have been compacted during long storage times. Rapeseed and other oily seeds are particularly susceptible. Wall friction can increase over time when grain swells due to moisture uptake. This can block flow along silo walls and create uneven discharge. Segregated fines zones in the centre of the silo can also create flow problems. Good silo design with sufficient cone angle and smooth internal surfaces is fundamental for preventing flow problems. For existing silos, flow aids such as vibrators or air cannons may be necessary.

Grain dust is explosive. Concentrations above 40-60 grams per cubic metre of air can be ignited by sparks, hot surfaces or electrostatic discharge. Dust explosions in grain silos have caused serious accidents and fatalities globally. Self-ignition is another risk. Biological activity in moist zones can generate enough heat to ignite the grain. Temperatures above 55°C in the grain mass should trigger immediate action. The ATEX directive sets strict requirements for equipment and work operations in explosive areas. All maintenance and cleaning activities in grain silos must be planned and carried out in accordance with applicable safety regulations.

Thorough cleaning of grain silos between storage seasons is essential for maintaining good hygiene and preventing pest problems. All grain residues, dust and cobwebs should be removed from internal surfaces. Blue Power offers specialised cleaning of grain silos with equipment adapted to food industry hygiene requirements. Our methods effectively remove deposits and residues without damaging the silo surfaces. Contact us to plan cleaning of your grain silos before the next storage season.