Adding milk to your breakfast cereal is a food science experiment in disguise.
Although food science may not be on your mind during an early morning breakfast, soggy corn flakes or oatmeal that is too thick may cause you to wonder why cereals absorb milk. Understanding the technology and science behind breakfast cereals can help you make that perfect hot oatmeal, or help you choose a cold cereal that suits your preferences.
Identification
Cereals, also called grains or cereal grains, are the seeds of grasses. Common cereal grains include wheat, oats, rice, corn, rye and barley. The core of these seeds is primarily carbohydrate in the form of starch, long chains of glucose molecules.
Starch
It is mostly the starch in cereal that absorbs liquid. The starch granules of each type of grain have a characteristic size and configuration, which affect how much liquid is absorbed and how fast absorption takes place. Oats and rice absorb twice their volume in liquid; wheat, corn and barley absorb three to four times their volume.
Absorption by Gelatinization
In a process called gelatinization, heat causes these starch granules to attract and trap liquid, whether it be water or milk, in their structure. The granules swell with milk, and smaller starch molecules diffuse out of the granules, trapping additional milk between the granules, and the mixture becomes thick. Hot breakfast cereals like oatmeal, cream of wheat or cream of rice, show this process clearly. Flaked cereals also absorb milk by gelatinization.
Absorption into Air Spaces
Other cold breakfast cereals absorb some milk by gelatinization, but most of the milk is absorbed into air spaces created in the cereal during processing. The two basic processes are puffing and extrusion. Puffing is used for whole grains much in the same way we make popcorn from whole grains of corn. Shaped cereals, such as spheres or donuts, are extruded from single or multiple types of grains that have been finely ground or milled.
Puffed Cereal Process
A Malt-O-Meal plant in Tremonton, Utah, which opened in 2004, has a gun puffing system which treats grain with heat and steam pressure inside the "gun." When the gun is fired toward the collection bin, the grains puff up with the release of pressure and steam, and the heat immediately cooks it. Puffing creates the air spaces that absorb milk.
Extruded Cereal Process
An extruder consists of a screw rotating inside a cylinder to mix the milled grains and liquid ingredients. The screws push the mixture, under pressure, along the length of the cylinder to the end, where it is forced, or extruded, through an opening of the desired shape. This is similar to a pasta maker used in home kitchens, except that the contents are under pressure and heat, so that when the mixture exits it immediately puffs, cooks, and becomes solid. Again, this leaves air spaces in the cereal that can absorb milk.
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