During the fall and winter, the exterior grain in a bin cools but the interior grain remains warmer. This difference in temperature develops slow moving air currents that carry moisture to the top of the grain pile near the center of the storage bin. As the air cools when it reaches the grain surface the air carries less water vapor and the moisture can condense on the grain surface. The potential for damage is greatest in bins that have not been leveled and have a peak near the middle of the grain pile. Producers should check stored grain on a regular basis during the storage season.
Mechanical aeration is the easiest way to mange moisture and temperature in stored grain.
Maintaining Stored Grain Quality, CIS 518.