Gluten is made of two families of proteins, called gliadin and glutenin, that naturally occur in wheat and several related grains. These proteins sit dormant inside the grain until they come into contact with water, at which point they link together to form a stretchy, elastic network. That network is what gives bread dough its chew and structure. Gluten-forming proteins make up roughly 70% to 75% of the total protein in a wheat kernel, with the rest being non-gluten proteins that play smaller roles.
The Two Proteins Inside Gluten
Gliadin and glutenin do very different jobs, and the balance between them determines how dough behaves. Glutenin molecules form large chains stabilized by strong chemical bonds between sulfur atoms (called disulfide bonds). These chains are responsible for elasticity: when you stretch dough and it springs back, that’s glutenin at work. Gliadin, on the other hand, acts more like a lubricant. It’s a smaller, single-unit protein that slides between the glutenin chains, giving dough its ability to flow and stretch without snapping.
The ratio of these two proteins directly controls the texture of whatever you’re baking. Higher gliadin content makes dough more extensible and soft, which is why cake flour (lower in glutenin) produces tender crumbs. Higher glutenin content makes dough tougher and more resistant to deformation, which is exactly what you want in a chewy bagel or a crusty loaf of bread. Bread flour is specifically milled from wheat varieties that lean toward more glutenin.
How Water and Kneading Build the Network
Gliadin and glutenin exist as dry, separate storage proteins packed inside the grain’s endosperm. They don’t become “gluten” until you add water. Hydration allows the proteins to unfold and begin interacting with each other through a combination of forces: hydrogen bonds, electrical attractions between charged regions, and the tendency of water-repelling parts of the molecules to cluster together.
Kneading or mechanical mixing takes this further. The physical force promotes the conversion of loose sulfur-containing groups into strong disulfide bonds, essentially welding glutenin chains into longer and longer polymers. Repeated kneading also strengthens the weaker, non-permanent bonds between molecules, giving dough greater overall strength and resistance to tearing. This is why under-kneaded dough tears easily while well-kneaded dough stretches into a thin, translucent sheet (the “windowpane test” bakers use).
The direction of mechanical force matters too. Stretching dough in two directions, rather than one, creates a more interconnected gluten network with greater strength. That’s part of why techniques like laminating or folding dough repeatedly produce such different textures from simple mixing.
Which Grains Contain Gluten
Wheat is the primary source, but gluten or gluten-like proteins also exist in barley and rye. The storage proteins in barley are called hordeins, and in rye they’re called secalins. These proteins are structurally similar enough to wheat’s gliadin and glutenin that they trigger the same immune reactions in people with celiac disease and are classified under the same regulatory umbrella. Triticale, a wheat-rye hybrid, contains both types.
Oats are a more complicated case. They contain a related protein called avenin, which is structurally distinct from wheat gluten but not entirely harmless for everyone with celiac disease. Research published in the journal Gut found that roughly a third of celiac patients experience acute immune activation and symptoms like nausea after consuming purified oat protein. About 3% of patients are “super-sensitive” and can have severe reactions resembling those triggered by wheat. For the majority, though, oats don’t cause intestinal damage even over several weeks of regular consumption. This is why many celiac guidelines allow oats but recommend starting cautiously.
Rice, corn, millet, buckwheat, quinoa, and sorghum do not contain gluten-forming proteins.
Why Gluten Triggers Celiac Disease
The immune reaction in celiac disease comes down to specific sequences of amino acids within gliadin. Human digestive enzymes have trouble fully breaking down gliadin because it contains unusually high amounts of two amino acids, proline and glutamine, arranged in repetitive patterns. One well-studied toxic fragment is just 11 amino acids long, ending in the sequence PSQQ, a motif that repeats throughout the gliadin molecule. These partially digested fragments survive the journey through the stomach and small intestine intact.
In people with celiac disease, immune cells in the gut lining recognize these fragments as threats and mount an inflammatory response. Over time, this damages the finger-like projections (villi) that line the small intestine and absorb nutrients. The reaction is tied to specific genetic markers that about 30% to 40% of the general population carries, though only a small fraction of those people actually develop celiac disease.
What “Gluten-Free” Actually Means
In the United States, the FDA requires that any product labeled “gluten-free,” “no gluten,” “free of gluten,” or “without gluten” contain less than 20 parts per million of gluten. That threshold was chosen because it’s the lowest level that can be reliably detected using validated testing methods. For context, 20 ppm means fewer than 20 milligrams of gluten per kilogram of food, a trace amount that research suggests is safe for the vast majority of people with celiac disease.
Products made from inherently gluten-free grains like rice or corn can still be contaminated during processing if they’re milled in facilities that also handle wheat. The “gluten-free” label confirms the final product has been tested or controlled to stay below that 20 ppm line, regardless of what grain it started as.