The germ of a cereal grain is the part that develops into a plant; it is the seed embryo. Along with bran, germ is often a by-product of the milling that produces refined grain products. Cereal grains and their components, such as wheat germ oil, rice bran oil, and maize bran, may be used as a source from which vegetable oil is extracted, or used directly as a food ingredient. The germ is retained as an integral part of whole-grain foods. Non-whole grain methods of milling are intended to isolate the endosperm, which is ground into flour, with removal of both the husk (bran) and the germ. Removal of bran is aimed at producing a flour with a white rather than a brown color, and eliminating fiber, which reduces nutrition. The germ is rich in polyunsaturated fats (which have a tendency to oxidize and become rancid on storage) and so germ removal improves the storage qualities of flour.