In whole-grains, the plant's cellular walls protect nutrients from oxidation, just like the skin on an apple protects it from oxidation. The process of oxidation begins to occur as soon as grain is ground or you bite into the apple, exposing the cell's contents to oxygen in the air. With the apple, it is very obvious because you see the apple turning brown but with grain, it is not as obvious but the process is the same. 

Flour that is several days (or more) old, has been exposed to oxygen that inevitably diminishes its nutritional value. The way to get full nutrition from whole grain foods is to mill them when you need them, right in your kitchen. Modern high-speed grain mills make it fast and easy to enjoy the freshest, best tasting and most nutritious food imaginable!

If you already own a Kitchen Aid mixer, you can purchase an attachment for milling grains. Or you can google “Grain Mill” for different options.