To ensure safe storage, the moisture content of food grains at the time of harvesting should not be higher than 14%. This moisture content threshold is generally considered safe to prevent spoilage, mold growth, and insect infestation during storage. Keeping the moisture content below this level helps in preserving the quality and preventing deterioration of food grains over time. It is important to note that specific moisture content requirements may vary for different types of food grains, so it is advisable to follow appropriate guidelines and recommendations for each specific crop.