When bakers begin discussing flour quality, the conversation quickly turns to gluten. During mixing of wheat flour and water, gluten forms. Gluten becomes the elastic framework of dough; it entraps the gas produced by fermentation and results in leavened dough.
Like other proteins, gluten becomes hard and dry on exposure to heat during baking (denaturation). Gluten denaturation, combined with starch gelatinization, contributes to the structure of most baked products.
Not all protein in flour is gluten-forming. The percentage of protein listed in the chemical composition of flour includes all proteins, irrespective of whether they are gluten-forming or non-gluten forming. Whole wheat flours contain more protein than refined flours, such as straight grade or patent flours. However, whole wheat flours produce a loaf of bread with smaller loaf volume. Bran and germ are high in protein of the non-gluten forming type. Although these increase the total quantity of protein in whole wheat flours, they decrease the proportion of gluten-forming proteins.
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