Maturity can best be judged by checking moisture content, using a moisture meter. Remember that even grain that is mature will contain excessive moisture just after a rain. There is never enough time at harvest, but a brief waiting period to allow grain to dry before combining will pay off later by preventing fungi from potentially spoiling the larger harvest in storage. Grain left in the field after physiological maturity will also begin to grow fungi due to insects, bird damage, and rain. Plants that have lodged, allowing ears to come in contact with the soil, may serve as sources of contamination, so adjusting combines to avoid picking up lodged ears will help prevent spoilage later.
Moisture is the main reason for spoilage of grains in storage.
Check bins for leaks, and stop rain from getting in. Hot pockets in the bin are a sign of leakage, and when the bin is emptied, these areas of caked grain will be obvious. Try not to mix spoiled grain with sound grain. Contaminated grain enclosed in a grain bin is a potential health hazard in the form of spores in the air. Always wear a dust mask if you must enter a grain bin.