There are two kinds of protein protein in flour, which are usually called "gluten" and "gliadin" respectively. In the water, they will gather together. When flour is put into water to "scrub", starch goes into the water, and these protein molecules run together and connect with each other under the mechanical action, which becomes "gluten protein".

Gluten is the decisive protein in gluten. There are many cysteines in gluten. This amino acid has a sulfhydryl group, which is a group with a hydrogen atom on the sulfur atom (-SH). This hydrogen atom is not honest, and he always wants to run away from home. In the process of kneading dough, if two sulfhydryl groups meet, their respective hydrogen atoms are likely to escape successfully. The remaining two sulfur atoms are connected together-this connection is chemically called "disulfide bond", which means that two sulfur atoms are connected. Once disulfide bonds are formed, it is not easy to open them, and two gluten molecules are connected to form a larger molecule. Because there are many such cysteines in each gluten molecule, each of them may form an alliance with other gluten molecules, so an intricate "relationship network" is finally formed. Such a protein network, when subjected to external forces, such as human hand pinching, tooth biting and so on, can produce certain deformation and keep opening.

Toast generally uses high-gluten or medium-gluten flour close to high-gluten. Protein content in flour is high, and gluten is the main ingredient. This kind of flour forms a strong network, which can trap more and bigger bubbles, so it can get a soft texture.

Protein content in rice is very low, generally below 7%. Moreover, most of the protein are different from gluten and lack the ability to connect with each other easily. Therefore, these protein can't form a network structure like wheat flour, and they can't make soft "rice bread", but they can only make rice cakes that are not stiff and not so soft.