Among grains, wheat flour is unique because it has the potential to produce gluten, a protein that imparts strength and elasticity to dough and influences the texture of baked goods. The gluten content of flour depends on whether the flour is made from hard or soft wheat; hard wheats are higher in protein than soft wheats, and thus produce more gluten. Most flour is a mixture of hard and soft wheat.
Because the production of flour isn’t standardized, flours from two manufacturers may use different milling procedures and consist of different blends, which will produce varying results in the kitchen. For example, all-purpose flours sold in the southern region of the United States contain a higher proportion of soft wheat, good for making the light, airy biscuits that are popular there. In northern states, by contrast, the preference is for breads rather than biscuits, and the all-purpose flour used in breadmaking contains a higher proportion of hard wheats.
Refined white flour consists of the ground endosperm of the wheat kernel. White flour is popular because it produces lighter baked goods than whole-wheat flour and has an unequaled ability to produce gluten. When the bran and germ are removed from the wheat kernel, vitamins and minerals are decreased, along with dietary fiber. Therefore, most white flour is enriched to replace some of the missing nutrients. If a flour has been enriched, the label will say so. There are many types of white flours, including:
- All-purpose flour (plain, white): Made from a blend of hard and soft wheats, this type of flour has a “middle of the road” protein and starch content that makes it suitable for either breads or cakes and pastries. All-purpose flour is available pre-sifted. This aerates the flour to make it lighter than standard all-purpose flour. However, all flour, whether labeled pre-sifted or not, has a tendency to settle and become more compact in storage, so the benefit of pre-sifting isn’t always apparent.
- Bleached flour: When freshly milled, flour is slightly yellow. To whiten it, manufacturers could let the flour age naturally, but most choose to speed up the process by adding chemicals, such as benzoyl peroxide or acetone peroxide, to bleach it. This process gives the flour more gluten-producing potential, but naturally aged flours develop more gluten as well.
- Bread flour: This is made entirely from hard wheat. A high gluten content helps bread rise higher because the gluten traps and holds air bubbles as the dough is mixed and kneaded. It’s also available in whole-wheat form.
- Bromated flour: Some manufacturers add a maturing agent such as bromate to flour in order to further develop the gluten and to make the kneading of doughs easier. Other maturing agents include phosphate, ascorbic acid, and malted barley.
- Cake flour: Finer than all-purpose flour, cake flour is made entirely from soft wheat. Because of its low gluten content, it is especially well suited for soft-textured cakes, quick breads, muffins, and cookies.
- Durum flour: Since it has the highest protein content of any flour, durum flour can produce the most gluten. It is frequently used for pasta.
- Farina: Farina is milled from the endosperm of any type of wheat, except for durum wheat (which is milled to make semolina; see below). Farina is primarily used in breakfast cereals and pasta.
- Gluten flour: Made so that it has about twice the gluten strength of regular bread flour, this flour is used as a strengthening agent with other flours that are low in gluten-producing potential.
- Instant flour (instant-blending, quick-mixing, granulated flour): Instant flour pours easily and mixes with liquids more readily than other flours. It is used to thicken sauces and gravies, but is not appropriate for most baking because of its very fine, powdery texture and high starch content.
- Pastry flour (cookie flour, cracker flour): This flour has a gluten content slightly higher than that of cake flour but lower than that of all-purpose flour, making it well-suited for fine, light-textured pastries.
- Self-rising flour: Soft wheat is used to make this flour, which contains salt, a leavening agent such as baking soda or baking powder, and an acid-releasing substance. However, the strength of the leavener in some flours deteriorates within two months, so purchase only as much as you need to use during that period. Self-rising flour should never be used in yeast-leavened baked goods.
- Semolina: This is the coarsely ground endosperm (no bran, no germ) of durum wheat. Its high protein content makes it ideal for making commercial pasta, and it can also be used to make bread.
Since roller milling separates the bran and the germ from the endosperm, the three components actually have to be reconstituted to produce whole-wheat flour. (The germ and bran are visible in the flour as minute brown flecks.) You may also find it called graham flour in the supermarket.
Because of the presence of bran, which reduces gluten development, baked goods made from whole-wheat flour are naturally heavier and denser than those made with white flour. Many bakers combine whole-wheat and white flour in order to gain the attributes of both. Whole-wheat pastry flour is also available.
For stone-ground whole-wheat flour, the kernels of wheat are crushed between two heavy, rotating stones, so that the bran and germ remain. Because oil in the germ is released during this process, stone-ground flour is more susceptible to rancidity. Nutritionally, there is no difference between stone-ground whole-wheat flour and roller-milled whole-wheat flour.
In addition to regular whole-wheat flours, there are a number of whole-grain flours made from close relatives of wheat, including:
- Kamut flour: Because of its very low gluten content, this flour is well tolerated by many people with wheat allergies. Use it for bread baking.
- Spelt flour: Made from the ancient grain spelt, this low-gluten flour also is well tolerated by many people with wheat allergies. Use it for bread baking.