Aeration

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 - FALL AND WINTER

 

 

 

 *% 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:

 

Heated Air Grain Dryers

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 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.

 

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.

 

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.

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.  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