Bread has been part of the human diet since prehistoric times. Early man pounded native grasses or grains into meal, added water and baked the resulting paste on a hot stone or in the ashes of a fire. The first bread was flat, unleavened and tough, but it became a staple in many early cultures. The discovery that adding yeast to the meal mixture improved flavor, texture and volume changed bread forever. Today the varieties of breads available around the world seem endless. Dense and chewy pumpernickle, mouthwatering Italian focaccia, rich and flaky croissants and the simple tortilla are but a few of the delicious breads that bring much pleasure to everyday meals.

Breads fall into one of three main categories depending on the leavening agent. Yeast-leavened bread makes up much of the bread available in bakeries and supermarkets. It can also be made at home. Although it requires some time to make, hot bread from the oven is a wonderful reward for your labors. Quick breads are leavened with baking powder, baking soda or steam. As their name suggests, they are quick and easy to make. (See Bread, Quick or additional information.) Unleavened breads, such as Middle Eastern lavash, Jewish matzo and Indian chapati, remain a tradition in many cuisines around the world.

Yeast breads contain yeast as a leavening agent. They require stirring or kneading to develop gluten, the protein in wheat flour that gives bread its structure. There are two types of yeast breads: yeast-batter breads and yeast-dough breads. Yeast-batter breads call for stirring and beating rather than kneading because ingredients form a soft dough that is too sticky to knead by hand. Yeast-dough breads are kneaded to produce breads with a chewier texture, finer grain and more volume. These doughs are less sticky and easier to handle than batter breads. They ususally become smooth and elastic with kneading. Sweet-yeast doughs are softer and stickier than regular yeast doughs because they contain more sweeteners and fat. Sweet-yeast breads may also be batter breads.

While baking yeast breads can be very satisfying, it is a lengthy process. Frozen yeast doughs and hot roll mixes are readily available and can simplify your life. They are an especially good choice for pizza crusts and dinner rolls.

Wheat flour is the essential ingredient in all breads because it contains the important protein called gluten. When mixed with liquid and stirred or kneaded, gluten stretches and forms a network of strands that catches the carbon dioxide bubbles produced by yeast. This network helps the dough rise and expand, giving the bread its structure. Most yeast bread is made with either bread flour or all-purpose flour. If you choose to substitute one flour for the other, be aware that the quantities used may differ slightly. Rye flour is low in gluten and must be combined with bread flour or all-purpose flour to produce a loaf that rises well and is not too dense. Whole wheat flour is usually used in combination with bread or all-purpose flour to avoid overly dense or poorly risen loaves. (The bran in whole wheat flour interferes with gluten development.)

Liquids are required in yeast breads to dissolve and activate the yeast and moisten the flour so gluten can develop. Most recipes have at least some water; other liquids contribute differently to a bread's flavor and texture. Water provides a chewy interior and crisp crust. Milk gives bread a mild, sweet flavor and soft, creamy texture; it also keeps breads fresh longer. Buttermilk adds a tangy flavor and light texture.

Active dry yeast contributes flavor and aroma in addition to leavening. One package of yeast contains thousands of microscopic living plants that are activated by warm liquid and fed by sugar and starch. Yeast releases carbon dioxide gas bubbles that become trapped in the gluten network, causing doughs and batters to rise and giving shape and texture to breads. Store packages of active dry yeast in a cool, dry place.

Temperature is an important factor when working with yeast. If the dissolving liquid is too cold, yeast action is retarded. Too much heat will kill the yeast. Use an instant-read thermometer to determine accurately if the liquid has reached the proper temperature.

The traditional method for using active dry yeast calls for warm liquids (105° to 115°F) to dissolve the yeast. The bubbly yeast mixture is added to the other ingredients as directed in the recipe. In an alternative method, the yeast is combined with a portion of the flour and the other dry ingredients. Warmer liquid (120° to 130°F) is then added. This method is slightly quicker than the traditional one, as the dissolving step is eliminated and the warmer liquid helps the yeast work faster.

Quick-rising yeast uses the alternative method and significantly reduces rising times. Quick-rising yeast may be substituted for regular yeast. Follow the package directions for recommended rising times. Both types of yeast are commonly available in individual packets containing about one tablespoon.

Granulated sugar and other sweeteners feed the yeast, as well as add their own flavors to the bread. They also help produce a browner crust and improve texture and tenderness. Brown sugar, honey, maple syrup and molasses are all used in breads; powdered sugar is not used because it contains cornstarch, which may affect flavor and texture.

Salt adds flavor to breads and also controls the action of the yeast. It slows the rising time, allowing the flavors of the dough to develop. Salt also strengthens the gluten, thus contributing to the texture.

Fats, such as butter, margarine and oils, impart flavor, richness and tenderness to breads. They help breads stay moist longer.

Eggs add flavor, color, strength and nutrients to breads. They give bread a golden color, tender crust and fine crumb.

This process ensures that the yeast is still alive before going ahead with the recipe. Yeast that is not living cannot make bread rise. To proof, sprinkle yeast and sugar over warm water using the amounts specified in each recipe and stir until the yeast is dissolved.

Let it stand 5 minutes or until the mixture is bubbly, indicating that the yeast is alive and releasing gas bubbles.

If the yeast does not bubble, it is no longer active. This may be the result of liquid that is too hot or yeast that is too old. (Always check the expiration date on the yeast package.) Discard the yeast mixture and start again with new ingredients.

Kneading is essential to developing and strengthening the gluten. Kneading also incorporates and homogenizes the ingredients in the dough. The dough will be sticky after all the ingredients are mixed in, gradually becoming smoother and elastic as it is kneaded. Bread dough may be kneaded by hand. For an inexperienced bread maker, an electric mixer with a dough hook attachment or a food processor can be used to mix and knead doughs quickly and efficiently.

To knead dough by hand, flour the kneading surface and your hands lightly before beginning in order to make the dough easier to handle. Flatten the dough slightly and fold it in half toward you.

Push the dough away from you with the heels of your hands in a rolling motion.

Rotate the dough one-quarter turn and repeat the folding, pushing and turning steps for the length of time specified by each recipe.

Letting the dough (or batter) rise means allowing time for the yeast cells to give off carbon dioxide gas. This process gradually expands and develops the dough in flavor and texture as well as structure. To prevent the kneaded dough from drying out and developing a crust, place the dough in a greased bowl and turn it over so the top is greased. (Batters rise in the bowls in which they are mixed.) Cover the dough with a clean kitchen towel and set it in a warm place (80° to 85°F) away from drafts until the dough has doubled or almost doubled in bulk. Use the time guidelines given in each recipe and test the dough as directed in the "Testing for Doubling" section.

Cold temperatures cause batters and doughs to rise slowly, offering the convenience of beginning a recipe one day and completing it later that day or the next day. For the refrigerator-rising method, batters and doughs are covered with greased plastic wrap and set in the refrigerator to rise for 3 to 24 hours. They are then brought to room temperature and shaped or baked as specified in the recipe.

To test if the dough has risen enough, lightly press two fingertips about one-half inch into the dough. The dough is ready if an indentation remains when fingertips are removed.

After the dough has risen, it is full of air pockets. To work out the excess carbon dioxide and redistribute the yeast, the dough is punched down. Push down the center of the dough with your fist.

Push the edges of the dough into the center.

With yeast-batter breads, the soft, sticky dough is stirred down with a wooden spoon rather than punched. The dough is now ready to rise again or to be shaped.

Bread recipes call for rolling, cutting or shaping the dough after it has risen. Lightly flour the rolling surface and rolling pin before working with the dough. If only a portion of the dough will be used at a time, keep the remaining dough covered with a towel to prevent it from drying out.

Change the look and texture of a bread's crust by varying the ingredients brushed on top of the loaf either before or after baking.

• For a shiny crust, brush with 1 egg white beaten with 1 tablespoon of water before baking.
• For a rich, tender golden brown crust, brush with milk or cream before baking.
• For a soft crust, brush melted butter or margarine over the crust immediately after baking.
• For a crisp crust, mist unglazed breads quickly with water several times during the first 10 minutes of baking.

To test breads for doneness, tap the tops of the loaves with your fingers or a wooden spoon. A hollow sound means the bread is done. A dull thud means that the bread is still moist inside and requires more baking. Remove yeast breads from pans immediately and cool completely on wire racks to prevent a soggy bottom.

Store yeast breads wrapped in plastic at room temperature. If the bread will be kept more than several days, refrigerate it. (Refrigeration dries out the bread somewhat, but it also slows the growth of mold.) Breads containing milk and fat last longer than those containing water and no fat. Yeast breads may be frozen by wrapping them securely in heavy-duty foil or by placing them in resealable freezer bags for up to six months. Seal well.

Reheat yeast breads, thawed at room temperature or directly from the freezer, by wrapping in foil and placing in a 350°F oven for 5 to 10 minutes. Microwave ovens may be used to thaw or reheat individual servings, but do not use them for whole loaves of bread, because portions of the bread may become tough before the entire loaf is heated through.