Cornmeal is flour ground from dried corn, is a common staple food, and is ground to fine, medium, and coarse consistencies. In the United States, the finely ground cornmeal is also referred to as cornflour. However, the word cornflour denotes cornstarch in recipes from the United Kingdom. Steel ground yellow cornmeal, common mostly in the United States, has the husk and germ of the maize kernel almost completely removed. It is conserved almost indefinitely if stored in an airtight container in a cool, dry place. Stone ground cornmeal retains some of the hull and germ, lending a little more flavor and nutrition to recipes. It is more perishable, but will store longer if refrigerated. However it too can have a fairly long shelf life of many months if kept in a reasonably cool place. It can also be used for cornmeal cakes. White cornmeal (mealie meal) is more traditional in Africa. It is also popular in the Southern United States for making cornbread. Blue cornmeal is made from the rarer blue corn or by adding blue food coloring. Cooking is the process of preparing food by applying heat, selecting, measuring and combining of ingredients in an ordered procedure for producing safe and edible food. The process encompasses a vast range of methods, tools and combinations of ingredients to alter the flavor, appearance, texture, or digestibility of food. Factors affecting the final outcome include the variability of ingredients, ambient conditions, tools, and the skill of the individual doing the actual cooking. The diversity of cooking worldwide is a reflection of the aesthetic, agricultural, economic, cultural, social and religious diversity throughout the nations, races, creeds and tribes across the globe. Applying heat to a food usually, though not always, chemically transforms it, thus changing its flavor, texture, consistency, appearance, and nutritional properties. Methods of cooking that involve the boiling of liquid in a receptacle have been practised at least since the 10th millennium BC, with the introduction of pottery.