Feeding whole kernel corn is satisfactory when cattle are essentially self fed and weather conditions do not interfere with frequent feed intake. Oats also are usually digested well when fed whole. A rather high percentage of most other grains tends to pass through whole without digestion, thus further processing is indicated. This is usually done with a hammermill. Factors influencing the fineness of the end product include screen size, hammermill size, power and speed, type of grain and moisture content of grain.
Grain is passed through rollers which are usually grooved on the surface.
Particle size varies from very small to very coarse and is influenced by roller weight, size of grooves, pressure and spacing, moisture content of the grain and rate of grain flow. Grain is exposed to steam for one to eight minutes prior to rolling. Sometimes this processing is also known as crimping or steam crimping. The steam softens the kernel, producing a more intact, crimped-appearing product than dry rolling. The moisture content of the grain is also increased slightly.