What Is Gluten and Why Does Dough Stretch?

Wheat grain stores two groups of proteins, glutenin and gliadin, as food for the seedling. In dry flour they sit inert. Add water and they unfold and start bonding to each other: the long glutenin molecules link end to end into chains, and the smaller, rounder gliadin molecules attach along them. The result is gluten, a stretchy, elastic mesh spread through the dough.

The two proteins give the dough two different qualities. Glutenin provides elasticity, the tendency to spring back when stretched. Gliadin provides extensibility, the ability to stretch without tearing. Bread needs both: enough elasticity to hold its shape as it rises, enough extensibility to let it rise at all. Flour is sold by protein content because that is roughly how much gluten it can make. Bread flour has 12 to 14 percent, plain flour 9 to 11, and cake flour as little as 7.

The mesh does not form fully by itself. When flour and water are first mixed, the proteins bond in a tangle, with strands pointing in every direction and many not linked at all. Kneading stretches and folds the dough over and over, which pulls the strands into alignment and gives them more chances to bond with their neighbours. Ten minutes of it turns a shaggy, tearing mass into something smooth that can be stretched thin enough to see light through, the windowpane test bakers use to judge when gluten is fully developed.

Time does part of the job too. Left alone, the proteins keep finding each other, which is why a no-knead bread that rests for twelve hours ends up with a well-developed structure despite never being worked. Salt tightens the network, which is why a dough without it feels slack, and fat or sugar interfere with it, which is why enriched doughs take longer to develop.

The reason any of this matters is gas. Yeast in a dough produces carbon dioxide, and without a gluten network the gas would simply escape. The elastic mesh traps it in thousands of tiny pockets, and as the yeast keeps working the pockets inflate and the dough rises. In the oven the gas expands further, the water turns to steam, and the loaf springs up before the heat sets the gluten and starch into a fixed sponge.

The strength of the network shows in the crumb. A strong, well-developed gluten holds large bubbles and gives the open, chewy interior of a baguette or a sourdough. A weaker one gives a finer, softer crumb. Stretch the same idea and you get pizza dough that can be spun without tearing, and the chewy pull of a good bagel, which is boiled before baking to set its surface gluten early.

Not every bake wants chew. A cake should be tender and a pastry should flake, and both are made by stopping gluten from developing. Cake recipes use low-protein flour, add fat and sugar early to coat the proteins, and warn against overmixing, all to keep the network short and weak. Shortcrust pastry rubs fat into the flour before any water goes in, so the proteins are waterproofed and can barely bond; the word short means exactly this, a texture that breaks rather than stretches.

Puff pastry sits between the two, with enough gluten to hold hundreds of separate layers and enough fat between them to keep the layers apart. Reading a recipe for how it treats gluten is the quickest way to understand why its instructions are the way they are. A rough guide:

• •Bread, pizza, bagels: high-protein flour, long kneading or resting, salt, little fat
• •Cakes, muffins: low-protein flour, fat and sugar early, minimal mixing
• •Shortcrust pastry: fat rubbed in before water, cold, handled briefly
• •Pasta: high-protein flour, kneaded firmly, rested so it can be rolled thin

For about one person in a hundred, gluten is a medical problem. In coeliac disease the immune system reacts to gliadin as though it were a threat and attacks the lining of the small intestine, causing damage that impairs nutrient absorption; the only treatment is avoiding gluten entirely, which means wheat, barley and rye. A smaller number have a wheat allergy, and some others report symptoms from gluten without either condition, which is still being studied.

For everyone else, gluten-free bread is simply bread without its structural protein, which is why it needs gums, starches and eggs to imitate the network and tends to be denser. The lesson of the science is that gluten is not a contaminant. It is the architecture of bread, and removing it means building the architecture some other way.

Gluten is the elastic network that two wheat proteins, glutenin and gliadin, form when flour is wetted and worked. Kneading aligns and strengthens it, it traps the gas that makes bread rise, and bakers control it deliberately: building it for bread and pasta, and blocking it with fat, sugar and gentle handling for cakes and pastry.