Types of wheat

Several types of wheat are grown today. They differ in their protein content and growing habit.

The most common species of bread wheat is Triticum aestivum. This wheat is high in protein and forms a strong gluten. Most of the wheat produced in North America is Hard wheat, which constitutes 75% of the total crop. Soft wheat makes up 20% and have less protein and form weaker gluten. Durum wheat is a different species that is mainly used to make pasta.

The classification of wheat growth habits and kernel color. Spring wheats are sown in spring and harvested in fall. Winter wheats are sown in the fall and harvested in summer. Red wheat gets its color from the presence of phenolic compounds, which the White wheat variety lacks, and it is often preferred for its sweeter taste.

Gas bubbles

Breads and cakes are aerated to the point that as much as 80% of their volume is empty space. Bakers use yeast and chemical leavenings to enhance the bubbles in their baked goods. It is important to note that leavenings do not create all of the gas present in the batter or dough. In fact, most of the bubbles form from air introduced when the baker kneads the dough, creams the butter and sugar, or whips the eggs. The carbon dioxide produced by leavenings is released into the water phase of the dough, diffuses to the bubbles already present, and merely enlarges them. Therefore, the initial aeration of doughs and batters strongly influence the final texture of the baked goods.

Starch

The word starch comes from a German root that means "to stiffen or make rigid." While starch has been used in paper making and textiles to stiffen, it has also served the same purpose bread making. Gluten proteins make only 10% of flour by weight, whereas starch makes up 70%. Starch granules absorb water, swell, and set to form the rigid bulk. They account for more than half the volume of dough. Though starch provides gives structure to bread, it also tenderizes it by penetrating and breaking up the gluten network. As carbon dioxide is produced, the rigidity of starch-formed walls stops the expansion of the bubbles. Pressure forces the water vapor inside to pop the bubbles and allow carbon dioxide to escape. As it does, a spongy network is left behind. This accounts for the crumbly texture of bread.

Starch is particularly important in batters where gluten proteins are too dispersed in water and sugar to contribute to the solidity of the cake.

Dough, batter, and texture

Wheat flour has characteristic liveliness and cohesiveness that set it apart from other cereal doughs. These characteristics make it possible for light, delicate loaves, flaky pastries, and silken pastas.

There are three basic elements at work: water, the flour's gluten proteins, and its starch granules. When integrated, these elements create cohesive mass.

Mixture of flour and water is called a dough or batter depending on the relative portions of the ingredients. According to Harold McGee, "doughs contain more flour than water and are stiff enough to be manipulated by hand. All the water is bound to the gluten proteins and to the surfaces of the starch granules, which are embedded in the semisolid gluten-water matrix. Batters contain more water than flour and are loose enough to pour. Much of the water is free liquid, and both gluten proteins and starch granules are dispersed in it." Once cooked, the starch granules absorb water, swell, and create a permanent sponge-like structure made up of millions of tiny air pockets.The term crumb refers to this network. Crust is the outer surface.

The texture of breads and cakes is light and tender because the protein-starch mass is divided up by millions of tiny bubbles. Pastries are flaky and tender because the protein-starch mass is interrupted by hundreds of layers of fat.

Controlling Gluten Strength

Gluten development and strength varies according to the product desired. For yeast-leavened breads and puffs, bakers need the tough qualities of gluten. For goods such as pastries, griddle cakes, and cookies, gluten needs to be controlled to avoid undesirable toughness. Here are some techniques and ingredients that affect gluten/gluten strength:

• Flour - high protein flour produces strong gluten, low protein and cake flours produce a weak one. Durum semolina produces a strong, plastic gluten preferable for pasta.
• Oxidizing substances - oxygen frees the sulfur groups at the end of glutenin proteins such that they are more available to react and form longer gluten chains that give dough greater elasticity and strength.
• Water - little water underdevelops gluten and forms a crumbly texture; a lot of water makes for less concentrated gluten and a softer, moister dough.
• Stirring/Kneading - mechanical actions stretch and organize the gluten network.
• Salt - the electrically charged ions of salt cluster around charged portions of the glutenin proteins allowing proteins to come closer to each other and form stronger bonds. Salt geratly strengthens the gluten network.
• Sugar - limits gluten development by diluting the flour proteins.
• Fats and oils - weaken gluten by bonding huydrophobic amino acids, thus preventing the proteins from further bonding to each other.
• Acidity - weakens the gluten network by increasing the repulsive forces between chains. This action is somewhat opposite of the effects of salt.

Gluten

Gluten proteins form long chains that stick to each other.

Gluten is an interconnected network of coiled chains made up of gliadins and glutenin proteins. Each of these proteins is around 1000 amino acids long. Gliadin chains fold onto themselves in a compact mass.  These proteins act as ball bearings for glutenin proteins. Glutenins have sulfur-containing amino acids at the end of their chains. Where gliadins only form weak bonds, glutenins form strong sulfur-sulfur bonds with each other, forming long chains. Amino acids in the glutenin chains also form weak temporary hydrophobic bonds that form the coil. The coiled and kinky gluten molecules makes the dough elastic. Thus when dough gets stretched out, the coils extend. When the tension is released, the kinks and coils reform, and the dough shrinks back to its original shape. These properties of plasticity and elasticity allow wheat dough to accomodate carbon dioxide gas without allowing it to escape.    

Bread 101

What qualifies as bread? On the most basic level, bread is the result from cooking a mixture of milled grains and water. Here is a quick run down of the most common ingredients in bread:

• Flour - Wheat flour is most commonly used in raised bread because it contains two proteins, glutenin and gliadin, which form gluten when combined with water. As the baker kneads the dough, the gluten develops and becomes elastic. This elasticity allows the incorporation of carbon dioxide gas into the dough.
• Starch is a carbohydrate that makes up 70% of the flour by weight. Starch granules release sugars that the yeast feed on. Starch reinforces gluten and absorbs water during baking, helping the gluten contain the carbon dioxide.  
• Water is the most important liquid in bread. It dissolves and activates yeast and blends with the flour to create gluten.  
• Yeast is a live, single-cell fungus that begins feeding on the sugars in flour and releases the carbon dioxide that makes bread rise. Yeast also adds many of the flavors and aromas associated with bread.
• Baking powder and baking soda are chemical leavenings that participate in the reactions between acidic and alkaline compounds that produce the carbon dioxide necessary to inflate dough or batter. These chemical leavenings act much faster than yeast, and are best used in quick breads.
• Salt slows rising time, which allows the flavor of the dough to develop. Salt also adds structure to the dough by strengthening the gluten, which keeps the carbon dioxide bubbles from expanding too rapidly.
• Eggs add food value, color, and flavor. They also make the crumb fine and the crust tender. Eggs add richness and protein.
• Fat in the form of butter, margarine, shortening or oil add flavor and moisture to bread. Fat slows moisture loss and helps bread stay fresh longer.
• Other liquids such as milk, buttermilk, cream or juice may be added for flavor or to enhance texture. Only add warm liquids to dry ingredients. Too cool liquids slow or stop yeast action. Too hot liquids destroy the yeast and prevent bread from rising.
• Sweetners such as sugar, brown sugar, honey, molasses, jams, and dried fruits may be used to add flavor and color to the crust.