Glassy, Glossy Foods

There is a special category of solid materials known as glasses, which lack the crystal structure that characterizes a true solid. Instead, their molecules, like those in liquid, are not ordered, but either are fixed into position or move only very slowly past one another. A large proportion of the foods that have crisp and crunchy textures owe these properties to their being in a glassy state and to the special effect this has on their mouthfeel. Unlike crystals, glasses can feel fragile or brittle in the mouth, which results in a crunchy mouthfeel rather than the sensation of crushing a hard crystal. An example is the contrast between eating a caramel and a crystalline sugar.