Things get a little more complicated when the bread must be made to last for days without going stale, to be inexpensive, to be consistent at any time of the year with grain from any supplier.
The simplest breads are made from flour, water, yeast, and salt. These breads are generally eaten the same day they are baked.
Wheat flour contains starch and protein, which form the structure of the bread. Two of the proteins in flour, gliaden, and the enzyme glutenin, form the elastic protein gluten when water is added and the mixture is stirred. Kneading the bread stretches the gluten into elastic sheets that can be filled with gas to form bubbles, making the bread lighter in texture.
The yeast supplies the gas. The yeast feeds on sugars in the flour, and produces carbon dioxide gas and alcohol as waste products.
The last ingredient, salt, is added to slow down the rate of fermentation of the yeast. This gives the baker a certain amount of control over the rising process, ensuring that the bread has the desired texture, and cooks evenly.
If the flour is allowed to age for about a month, its natural yellowish color will fade to white due to the effects of oxygen. This aging period can allow insects to spoil the flour, and is often eliminated by adding bleaching agents such as benzoyl peroxide.
Malted barley flour is often added to bread because it gives the yeast more nutrients (primarily sugars), and gives the bread a different taste. Malting a grain is the process of letting the grain soak in water until it starts to sprout. The young sprouting barley plant converts some of the starch in the barley endosperm into sugars. The barley is then cooked or ground into flour, which stops the sprout from eating the sugars, leaving them available to the yeast. Sometimes sugar, or high fructose corn syrup are added as yeast nutrients, or to make the crust of the bread brown more easily.
Flour made from soybeans is sometimes found in breads to give them added protein, and to change the texture of the bread. Soy flour absorbs water to make a gel, making the bread denser.
Some of the nutrients lost when the wheat germ and bran are discarded are returned to the flour by adding small amounts of vitamins and minerals. Commonly, the vitamins niacin, thiamine, riboflavin, and folic acid are added, along with the minerals iron and calcium.
Vegetable oils are added to breads to shorten the strands of gluten, to make the bread more cake-like. Adding fats or oils also keeps the bread from getting stale, allowing it to be kept longer than a day before being eaten.
What happens in bread to make it stale is the recrystallization of the starch. Fats and oils added to bread form a complex with the starch in its gelled form, and this slows down the recrystallization, keeping the starch in the flexible gel form.
Fats and oils, however, interfere with the gluten, making the gluten strands shorter, preventing the loaf from getting volume. Emulsifiers are commonly used instead of fats to control staling. Emulsifiers have a fatty acid at one end that can combine with the starch, and a water-loving end that helps to keep it dispersed in the dough. Emulsifiers aid in distributing fats and oils throughout the dough, so less fat or oil is needed.
Some emulsifiers commonly used in baked goods are:
Another way to control staling is to add humectant (water attracting) agents to the dough. To recrystallize, starch needs water.
By attracting water away from the starch, humectants keep it from recrystallizing, and at the same time add more moisture to the product. A moist bread tastes and feels better, and it weighs more without adding expensive ingredients. Thus a one pound loaf of bread that has a higher water content is less expensive than a drier one pound loaf.
Salt and sugar are good humectants. Sugars that are less sweet, such as dextrose (glucose) can be used for their humectant properties if sweetness is not desired.