Basic Yeast Bread Ingredients

Flour

Flour provides the structure for the product. The gluten (or protein) in flour, combines to form a web that traps air bubbles. Starch in the flour sets as it heats to add to and support the structure.

In yeast bread, the goal is to get a lot of gluten formation, since it forms a stretchy web that traps carbon dioxide and steam during baking. This gives bread its texture (also known as "crumb"). Fats and sugars help prevent gluten formation.

There is also some simple sugar available in flour and this feeds the yeast. If you have a bread recipe with no sugar source, that's okay—the yeast will have enough to "eat" from the flour alone. The rising times will be longer, though.

Bread flour is high protein flour. It produces bread that has a higher volume because it contains more stretchy gluten. Loaves made with bread flour rest for 10 to 15 minutes after rising and before shaping the loaves so the gluten relaxes a bit and the dough is easier to work.
All-purpose flour works just fine for most bread. This is convenient for the average home baker and the difference in gluten content between all-purpose and bread flour is typically just 1 percent.
Whole grain flours do not have as much gluten because there are other ingredients like bran and germ which get between the gluten molecules. This type of flour is usually combined with bread or all-purpose flour to make a better crumb.

Yeast

Yeast is a one-celled plant available in dried form, an instant blend, and live cakes. In yeasted bread, yeast multiplies and grows by using available sugars and water. At the same time, it gives off carbon dioxide and ethyl alcohol through a process called fermentation. As long as air is available, the yeast multiplies.

In bread recipes where the bread rises for a second time, you are told to "punch down" the dough. This breaks up small clusters or colonies of yeast cells so they can get in contact with more air and food. This is why the second rise is usually shorter than the first rise.

Whenever possible, try to use live yeast cakes. Many bakers believe that it results in a better flavor. The downside is that cake yeast spoils very quickly, so it's best when used within a day of buying it. You can also freeze cake yeast.
For most bakers, active dry yeast would be the second choice. It tends to produce a better flavor than instant yeast.
Instant-rise yeast has been genetically modified and is packaged with its own food supply. It becomes active instantly when it is rehydrated with liquid. This type of yeast is very convenient, but the rise is so fast that it doesn't allow much flavor to develop during fermentation.

Liquid

A liquid, such as water or milk, helps carry flavorings throughout the product. It helps form the gluten bonds and reacts with the starch in the protein for a strong but light structure.

Liquids also act as steam during baking, contributing to the tenderness of the product. Additionally, the yeast needs liquid in order to develop, reproduce, multiply, and form byproducts which make the bread rise.

Salt

Salt is an essential ingredient in bread and it's extremely important that it is measured carefully. If you're cutting salt from your diet, your bread is not the place to do it. Don't worry, though, most recipes typically use just 1 teaspoon.

Adding salt to bread dough strengthens gluten and enhances the flavor. In yeast bread, salt helps moderate the effect of the yeast so the bread doesn't rise too quickly. In this role, it is called a "retarder" because it slows down the yeast so the dough doesn't get out of control and has time to develop flavors.

Fat

The most common types of fat used in bread are oils, shortening, and butter. The fat coats the gluten molecules so they cannot combine as easily. This contributes to the finished product's tenderness.

Yeast bread that has a high proportion of fat to flour is much more tender, doesn't rise as high, and have a very tender mouth-feel. Fat also contributes flavor to the bread and helps it brown while baking.

How to Substitute Shortening for Butter and Vice Versa

Sugar

Sugar adds sweetness and contributes to the bread's browning. The main role for sugar in yeast bread is to provide food for the yeast.

As the yeast grows and multiplies, it uses the sugar, forming byproducts of carbon dioxide and alcohol, which give bread its characteristic flavor. Sugar tenderizes bread by preventing the gluten from forming. It also holds moisture in the finished product.

Eggs

Eggs are a leavening agent that is used in some bread recipes, but not all. When a lot of eggs are used, they contribute to the flavor of the finished product and often create a very rich bread.

The egg yolks also add fat for a tender and light texture. Yolks act as an emulsifier for a smooth and even texture in the finished product as well. In some bread, yolks are included along with whole eggs.

Sourdough Starter

Sourdough bread depends on a yeast and bacteria "starter." This is a mixture of flour, yeast, liquid, and bacteria that provide the signature sour flavor this type of bread is known for. The bacteria lowers the pH of the bread mixture, which adds to the flavor. Since the bread is more acidic (lower pH), this bread keeps longer than the average yeast bread.

You can make a starter in your own kitchen without adding any yeast if you do a lot of yeasted bread baking because the yeast cells are present in your kitchen. If you're new to working with yeast, however, you will want to add yeast to your starter.

On an interesting note, San Francisco sourdough bread can only be made in San Francisco. Scientists discovered that the bacteria in the bread was original to the area. A wild yeast native to San Francisco was the only type that would grow with these special bacteria.

Mixes are now made in that city and shipped to other parts of the country so you can make San Francisco sourdough in your home. Yet, that special bacteria and yeast will not grow in your home kitchen, as they do for ordinary sourdough starters.

How to Make Basic Sourdough Bread