All flours are made up mainly of carbohydrate, in the form of starch, and various types of protein.
Gluten forms a rubbery web-like structure within the dough; food scientists often refer to this structure as a 'gluten matrix'. In simple terms, this structure traps the carbon dioxide gas produced during fermentation, which causes the dough to rise.
Gluten is unique in having these gas-retaining qualities. Bread made with flour that contains little or no gluten will rise very little, if at all, as the gases released during fermentation will quickly escape from the dough through diffusion. The role of gluten in trapping gas in bread is complex and still not completely understood.
The gluten content of wheat flour varies between varieties. Wheat flour that is high in gluten is usually sold as 'strong flour' or 'bread flour'. Flour that is low in gluten is often packaged as 'plain flour'.
Want to find out more? Look at the chapter on ingredients in the book flour and water.
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