Gluten is a mixture of the two proteins gliadin and glutenin. Gluten is present in wheat flour, gray in color, and elastic in texture. Not present in barley, oats, or corn, gluten contributes the elasticity to dough, trapping carbon dioxide, and giving a desirable crumb structure on baking. The proportion of gluten in wheat flour varies from 8% to 15%; the level determines the suitability of the flour for different uses. The high gluten content of hard wheat is right for bread and pasta, while soft wheat (low gluten) is used for biscuits. Being insoluble in water, gluten can be washed out of flour; it is then used as an additive to chocolate and coffee. Sensitivity to gluten leads to celiac disease in children.