Gluten

A large percentage of the protein in wheat flour is gluten, though gluten isn’t a single substance, it is formed by the combinations of two groups of proteins: glutenin and gliadin.

If you looked under a powerful microscope, you’d see that gluten is made up of coiled-up strands that look like mini springs. As the gluten develops, the strands begin to uncoil and start to form links to other strands close by, joining together to form what looks like a net. As this microscopic mesh develops, forming more and more links, it becomes like bubble gum, able to trap gas. This stretchy network of gluten strands is the main building material of the walls of the holes we see in wheat bread.