Vicki Herbert, age 12, of Nashville, Tenn., for her question:
HOW IS WHITE FLOUR MILLED
Bread made with flour ranks as the world's most widely eaten food. People in many countries receive more than half of their nourishment from foods made with flour.
White flour made from wheat accounts for more than 90 percent of the flour produced in the United States today.
Wheat kernels, which form the raw material for flour, are made up of a tough covering called bran, a mellow inner part called the endosperm and a tiny new wheat plant called the germ. To make white flour, millers separate the endosperm from the bran and germ and then grind the endosperm into flour.
Cleaning machines first take all dirt, straw and other impurities from the grain. Then the wheat is moistened. The moisture makes the endosperm more mellow and the bran tougher.
The moistened wheat, which is then called tempered wheat, passes between a series of rough steel rollers that crush the endosperm into chunks. Pieces of bran and germ cling to the chunks of endosperm to form separate flakes.
Next the crushed grain is sifted. The tiniest bits of endosperm, which have become flour, pass through the sifter into a bin. Larger particles collect in the sifter.
Next the larger particles are put into a machine called a purifier. There, currents of air blow flakes of bran away from the remaining endosperm particles.
The endosperm particles are then repeatedly ground between smooth rollers, sifted and purified until they form flour.
In most mills, about 72 percent of the wheat eventually becomes flour. The rest is sold chiefly as livestock feed.
Newly milled flour is cream colored but some mills bleach it to make it white. Some mills also add chemicals that strengthen the gluten.
Wheat is rich in starch, protein, B vitamins and such minerals as iron and phosphorus. But the vitamins and some of the minerals are chiefly in the bran and germ, which milling removes from white flour.
Most millers in the United States and many other countries enrich their product by adding iron and vitamins to white flour made for home use.
Also, most bakeries use enriched flour or they add vitamins and minerals to dough made with unenriched white flour.
The enriching of white flour has undoubtedly helped millions of people avoid malnutrition since diseases caused by a lack of B vitamins were common in the United States before 1941. That year, the nation's bakers and millers began enriching white flour products. Today, few Americans suffer those diseases.