A cereal mill is a mechanical device that is designed to accept a quantity of whole, dried grains and grind them down into flour or to crack them into a more manageable state. There are two main types of cereal mill, a hand-operated mill and an electric mill, with some models having the option for either type of operation. Inside the mill, the whole grains can either be crushed with rolling wheels, smashed with impact blades or ground with burrs, with a few types of mills using a hybrid system that relies on an auger and a milling plate. Most mills have some type of restriction in what they will grind, with a distinction being made between soft grains, hard grains and oily grains that can leech enough oil over time to reduce the effectiveness of the grinding mechanism. There are many types of cereal mill available, with some focused on speed, others on convenience, and some that are more specifically designed to focus on keeping the grains below a certain temperature or on grinding wet grains.
The main goal of a cereal mill is to reduce the size of whole grains in some way. This could mean turning the grains into a fine powder that can be used as flour for baking, or it could involve cracking or splitting the grains so they can be softened in water and eaten more easily. The simplest type of mill is known as a stone mill or roller and is made from one stationary wheel and one moving wheel. The wheels can be made from stone, such as granite, but more often are made from composite materials or metal. The grain is milled by being crushed between the stones, allowing the finest grind of any milling method, although it cannot be used with oily grains.
A more common type of cereal mill uses a burr grinder. This is a wheel that has been studded with small, sharp teeth that break apart the grains as the wheel is rotated. A burr grinder can handle hard grains, but often is not capable of creating flour that is as fine as that created by a stone mill.
An inexpensive option that can be used in very small units is known as an impact cereal mill. This consists of two plates that have concentric circles of teeth mounted perpendicular to the plane of the plate. The teeth are placed so that, when the plates are rotated, they weave together but do not touch. As grains are fed between the plates, the pressure of the teeth breaks apart the grains. An impact mill can be very effective, although not all models allow for the grind size to be adjusted, and the plates themselves are sometimes subject to damage from harder grains or impurities in the grains, such as stones.
There are some issues that can arise while using a cereal mill. One is the heat generated from quickly grinding the grains, which may shorten the lifespan of the flour by heating the oils or reduce the natural amount of nutrients in the grains. Another common issue is the noise generated by the mill, which can be extremely loud in some electric models.
The size of a cereal mill can vary greatly. For home use, the mills can range in size from very small and compact — about the size of a coffee grinder — to extremely large, sometimes taking up an entire tabletop. Commercial mills can be as large as an entire room and operate with gas-powered motors.