The germ is the most nutritious portion of the wheat kernel and makes up only about 2 1/2% of its weight. It has a nutty flavor and is very oily, which causes it to turn rancid quickly. Wheat germ is the reproductive area or embryo from which the seed germinates to form the sprout that becomes the green wheat grass. The term "germ" comes from the word germinate, and does not refer to "germs" such as bacteria and viruses. Wheat germ is usually separated from the bran and starch during the milling of flour because the germ's perishable oil content limits the keeping time of the flour. Wheat germ contains very little of the sticky gluten protein to which many with wheat allergy react. Wheat germ oil, an extraction of the germ, is strongly flavored and expensive.