“Insects and molds are the main predators during storage of grains and growth of these insects and micro-organisms increases dramatically when the relative humidity inside the grain bins rise above 70% and temperature is above 25˚C. Prevention of insect and mold growth is a better option than the control measures, and if insect and mold growth couldn't be controlled at an early stage, there is the potential for total damage of the grain.”
Digvir S. JAYAS
University of Manitoba, Department of Biosystems engineering
Post-harvest losses of cereal grains during storage account for 1-2% in well managed systems and 20-30% in poorly managed systems. During harvest, the moisture content of grain is around 20-30%, and harvest temperature is 25-50˚C depending the growing region of the world. This harvested moist and warm grain should be dried and cooled before storage. Moisture content and temperature are the main factors that determine the length of storage time for storing grains without spoilage.
Insects and molds are the main predators during storage of grains and growth of these insects and micro-organisms increases dramatically when the relative humidity inside the grain bins rise above 70% and temperature is above 25˚C. Prevention of insect and mold growth is a better option than the control measures, and if insect and mold growth couldn't be controlled at an early stage, there is the potential for total damage of the grain.
There have been “Safe Storage Guidelines” for different types of grains at Canadian Grain Commission's website. You can find guidelines and related charts below.
The safe storage time of grains decreases with increase in storage temperature and moisture content of grains. Temperature gradients inside the grain bin lead to moisture migration and when moisture from warmer areas migrate to colder areas condensation could occur in cool grain near the top of the bin or on bin ceiling or wall due to moist warm air coming in contact with the cool surfaces. If the ventilation of bin is poor, the moist and warm air cannot be removed from the bin and can create favourable conditions for insect and mold growth.
Good management practices which help to reduce grain storage losses (CGC, 2014 & Manitoba Agriculture, 2014) are:
A) CLEAN BEFORE FILL:
Bins should be cleaned before filling with newly harvested grain. Perforated floors and air ducts also should be cleaned. Spilled and spoiled grain in and around the bins should be cleaned to avoid cross contamination and rodent activity. Spraying insecticides and fungicides inside the cleaned bins will help to eliminate carryover of insect and mold spores from the previously stored grains.
B) COOL AND DRY THE GRAIN:
Decrease the grain moisture to the safe storage level and cooling the grain below 15˚C will help to eliminate insect and mold development during storage. Aeration or chilled aeration is the process help to reduce the temperature. Drying process reduces the moisture content. Drying can be done with properly designed systems using either ambient air or heated air.
C) TURN THE GRAIN OFTEN:
Turning the grain inside the bin (moving from one bin to another) brings grain to average temperature inside the bin and eliminates temperature gradients and thus moisture migration.
D) CLEAN THE GRAIN:
Removing broken seeds, foreign materials and dockages before loading in to the bin will help for better air movement inside the bin as well as reduce insect and mold problems. Use of grain spreaders during filling of bins helps in distributing fines more uniformly and thus helps in reducing the risk of localised hot spot development. Use of spreaders however packs the grains thus increasing resistance to airflow and could reduce airflow through grains significantly because airflow output from a fan decreases as static pressure increases.
E) AVOID MIXING GRAINS:
Mixing newly harvested grains with the grain already in the bin has potential to create huge temperature and moisture gradients inside the bin and thus leading to increased chances of spoilage.
F) MONITOR CONTINUOUSLY:
Regular monitoring of grain moisture and temperature will help to identify the potential hazards on time, and take control actions in a proactively. Nowadays various types of temperature sensors, combination of temperature and moisture sensors are available in the market for continuous monitoring of grain bins.