Gluten is chiefly a mixture of two pro-teins which are found in cereal grains. When water is added to flour, the two proteins combine to form gluten. It is the presence of gluten in flour that helps all leavened breads, other baked foods and cakes not only to rise but, once risen, to hold their shape.
Wheat flour contains the highest pro-portion of gluten but the strength and elasticity of the gluten depends on where the wheat is grown. For example, Canadian wheat is ‘strong’ and so makes good bread; British wheat is ‘weak’ and is better for making cakes and biscuits . Manufacturers of bread and baked goods blend flours to the strength they require.
The flour sold in retail stores is generally plain or self-raising, unless otherwise specified on the package.