Peter Brown, age 12, of Columbus, Ohio, for his question:

HOW IS WHITE FLOUR MILLED?

Wheat kernels provide the raw material for flour. Each kernel contains a tough covering called the 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 germ and the bran and grind the endosperm into a powder. '

Before you start the milling operation, various cleaning machines remove dirt, straw and other impurities from the grain. Next the wheat is tempered or moistened. The moisture makes the endosperm more mellow and the bran tougher.

Next the 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 or form separate flakes. Then the crushed grain is sifted.

The smallest pieces of endosperm, which have become flour, pass through the sifter into a bin. Larger particles collect in the sifter.

Next, the larger pieces are put into a machine called a purifier. There, currents of air blow flakes of bran away from the 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. They may 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 then enrich their product by adding iron and vitamins to all white flour that is made for home use.

Most U.S. bakeries use enriched flour or they add vitamins to under enriched white flour.

The enriching of white flour has most likely helped millions of people avoid malnutrition. Diseases caused by a lack of B vitamins were common in the United States before 1941. Then that year, the nation's bakers and millers started enriching white flour products. Today, few Americans suffer those diseases.

Historians tell us that people were probably making a type of flour as far back as 15,000 B.C. They used rocks to crush wild grain on other rocks.

When farming started about 8,000 B.C., people started to grow such grains as barley, millet, rice, rye and wheat.

By the 1000s B.C., millers were grinding their grains between two large, flat millstones. Later, domestic animals or groups of slaves rotated the top stone to crush the grain.

In the 600s A.D., windmills were powering flour mills in northern Europe.

Milling improved greatly in England in 1780. That year, a Scottish engineer named James Watt built the first steam powered flour mill.

In 1802, a Philadelphia miller named Oliver Evans opened the first power mill in the United States.