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Flaked cereals are made directly from whole grain kernels or parts of kernels. Corn flakes are made with maize endosperm. The maize grits are pressure cooked with a solution containing sugar, malt (nonenzymatic), and salt. The cooked grits are partially dried to remove stickiness and then tempered for 24 hours to allow the moisture to equilibrate. The grits are subsequently submitted to flaking and toasting, where the moisture decreases to less than 3%, and the product is browned and blistered. After cooling, the flakes are sprayed with a solution of vitamins and minerals. To make wheat or rye flakes, the whole kernel is used and each kernel makes one flake. A heating step is applied before the flaking to plasticize the kernel. Instead of cooked grains, flakes may also be made from extruded pellets in a similar way.

Collapse of structure and formation of rubbery and crystalline states affects strongly physical properties of cereal products (Boitte et al. 2013). The mechanical and sensory properties of grain flakes are affected by water content. Crunchiness is lost upon water adsorption and it is attributed to the plasticizing effect of water. However, water adsorption has either plasticizing or antiplasticizing effect depending on the water activity (Gondek and Lewicki 2006).

The type of grain affects the internal structure of the product. For instance, corn flakes present a porous structure with thick, continuous and homogenous air bubbles, whereas wheat bran flakes have a heterogeneous structure with many discontinuities, cracks and ruptures. These structural differences influence the behavior of the products against compression. Fragile breaking of the matrix occurs in corn flakes, while dislocations of one piece of wheat bran against the others manifest in the wheat bran flakes (Gondek and Lewicki 2006).