Drying and Storage of Damp Grain


Aeration is the use of relatively low airflow rates to cool grain and eliminate temperature and moisture differences in the storage bin. Aeration may be used with field-dried grain or with grain that is harvested damp, then dried and cooled in a heated air dryer. In both cases, temperature and moisture content variations may exist in the grain, or the grain may be too warm to store safely. Variations in grain temperature are also caused by changes in the outside air temperature after the grain is stored.
Warm air rising in the centre of the bin cools when it reaches the cold grain near the surface. This results in an increase in moisture content near the surface, which can lead to rapid spoilage. Crusting on the surface of stored grain is a common symptom of moisture migration. Significant migration can occur in cereal grains at moisture contents as low as 12 per cent, or as low as 8 per cent in oilseeds if they are placed into storage at high temperature and not cooled.

moisture migration in stored grain
Table 8 - Summary of basic recommendations for drying and cooling processes in stored grain
Process % above "dry"* Recommended
airflow rates (L/s) m3
 Recommended Minimum
Perforated Floor Area (%)
Transfer for final storage
Aeration 0 1-2 15% no
 Air Drying
1-6 5-30** 100 no
Dryeration 2-3 5-10 40 yes 
100 no
In-Storage Cooling 1 5-10 40 no
 *% above "dry" is the number of moisture percentage points above "dry" at which the grain is placed into the bin. Example: For dryeration, wheat is placed into the bin at up to 17% moisture (14.5 + 2.5 = 17%).
** Recommended minimum airflow rate for drying grain depends on grain moisture content and harvest date.

Satisfactory performance of an air handling system depends on the selection of proper equipment, adequate sizing, proper installation and good management (Table 8). Three requirements must be met to ensure proper performance:
  1. Selection of a fan or combination of fans that deliver the required air flow at the necessary static pressure.
  2. Proper sizing and arrangement of the perforated duct surface area or perforated floor area to deliver the air uniformly.
  3. Proper sizing (cross-sectional flow area) of the ducts, fan transition, and bin exhaust vents.

Heated Air Grain Dryers

Advantages of Grain Drying: Longer Harvest Season
A grain dryer can substantially increase the number of available harvesting hours and days in most areas, and could also reduce the overall investment in machinery. A smaller combine plus a dryer could be used instead of buying a second combine or trading up to a larger one. For a producer relying on custom harvesting, a grain dryer can be helpful in getting harvesting done early.
Earlier Harvesting
Earlier harvesting is possible when a grain dryer is used. Wheat, oats and barley can be threshed at 20 per cent moisture content (MC) and then dried without loss of quality, grade or germination. When compared with harvesting at 14 per cent, there may be a difference of only one or two days in mid-August, but by mid-September it may be 4 days or more. If a wet spell occurs, the differences could be much greater. Early harvesting may allow a producer to harvest nearer to the maximum ‘dry’ moisture content, which results in the highest weight of grain for sale. Harvesting early also allows a producer to do a better job of weed control through timely chemical application and tillage practices.
Reduced Field Losses
Weather damage and losses caused by wildlife can be reduced by harvesting at the tough or damp stages. Losses in grade and weight due to weather can be substantial. Harvesting before, instead of after, a rainy spell can therefore result in a considerable saving. Straight combining of some crops, such as sunflowers and corn, is a necessity, and if these crops are harvested damp, field losses are greatly reduced. A dryer in the system may also make it feasible to straight combine other crops. Overdrying of crops in the field, which leads to shattering and crop loss, can also be prevented by earlier harvesting. A dryer is therefore an alternative that could be considered to reduce field losses.
Eliminate Spoilage in Storage
When tough or damp grain is harvested and not dried, long-term storage frequently results in grain spoilage. Moisture migration within grain bins can make slightly tough or even dry grain unsuitable for storage. Spoilage problems caused by hot spots and insect infestations can be reduced or eliminated by proper drying and aeration in storage.
The initial cost of a dryer is one of the major deterrents to grain drying. Where only small amounts of grain are to be dried each year, the initial cost should be a primary consideration. Where large amounts of grain are dried, fuel efficiency becomes the most important factor.
The labor and inconvenience of drying are also deterrents on many farms where no centralized grain storage facility exists. To obtain maximum benefits from a grain dryer, it is necessary to set up a well organized system for grain handling and storage.

Testing for Heat Damage
Various tests may be conducted to find the highest acceptable drying temperatures for a particular grain and dryer. If the grain is to be used for seed, a germination test should be used. In addition, a sample of grain should be taken before drying for testing to help determine whether there was any change in the germination rate during the drying process. Commercial grains other than for seed (milling wheat, malting barley and oilseeds) are tested free of charge for heat damage by the Canadian Grain Commission. Two samples (minimum of 500 g each), one taken before and one after drying, should be sent to the Grain Research Laboratory, Canadian Grain Commission, 303 Main Street, Winnipeg, Manitoba, R3C 3G8. The samples should be representative of the grain going in and coming out of the dryer. If the grain quality is unchanged, a higher temperature can be tried and two more samples sent in for testing. Several companies that purchase oilseeds, corn and grain for seed also conduct tests for heat damage. Check with the purchaser at the start of drying to ensure that the dried grain meets their standards.
For more information refer to Manitoba Agriculture, Food and Rural Development fact sheet Grain Aeration and Unheated Air Drying and Agriculture Canada’s fact sheet Heated-Air Grain Dryers.

Storage Moulds

Storage moulds are types of fungi that grow in stored grain at temperatures as low as -5°C and moisture contents at/or above those given in Table 8. Detrimental changes in grain appearance and quality occur in storage. Byproducts of most storage moulds are mycotoxins, such as ochratoxin, which are poisonous to humans and animals. Infections by storage fungi are promoted by high temperatures, seed injury, green crop or weed debris and especially moisture. Grain in storage should be monitored periodically for evidence of heating and off-odours which are indications of mould growth.