Beef, the meat of an adult (over 1 year) bovine, wasn't always as popular as it is today. America has had cattle since the mid-1500s, but most immigrants preferred either pork or chicken. Shortages of those two meats during the Civil War, however, suddenly made beef attractive and very much in demand. Today's beef comes from cows (females that have borne at least one calf), steers (males castrated when very young), heifers (females that have never borne a calf) and bulls under 2 years old. Meat packers can request and pay for their meat to be graded by the U.S. Department of Agriculture (USDA). The grading is based on three factors: conformation (the proportion of meat to bone), finish (proportion of fat to lean) and overall quality. Beginning with the best quality, the eight USDA grades for beef are Prime, Choice, Select, Standard, Commercial, Utility, Cutter and Canner. The meat's grade is stamped within a purple shield (a harmless vegetable dye is used for the ink) at regular intervals on the outside of each carcass. A powder is a dry, bulk solid composed of a large number of very fine particles that may flow freely when shaken or tilted. Powders are a special sub-class of granular materials, although the terms powder and granular are sometimes used to distinguish separate classes of material. In particular, powders refer to those granular materials that have the finer grain sizes, and that therefore have a greater tendency to form clumps when flowing. Granulars refers to the coarser granular materials that do not tend to form clumps except when wet. 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. The most traditional clothing when cooking is aprons.