Oil and water are combined mechanically or with the addition of a third substance.
The adage "like oil and water" describes two things that do not mix. Water is a polar molecule and is attracted to hydrophilic, or "water loving" substances. Oil is non-polar, which makes it hydrophobic, or "water fearing." The two do not mix in nature, but homogenization applications are used in various industries to combine oil and water into a uniform substance.
Homogenization
The term "homogenization" is most recognized as an application of milk production. Milk is homogenized, or made uniform, through a mechanical process. Milk is a solution of oil and water. Before homogenization, fat globules rise to the top of the fluid. In the process of homogenization, the milk is passed through a fine mesh sieve that breaks down the fat globules so they disperse evenly throughout the water. This produces a creamy, uniform milk product.
Emulsification
Emulsification is simply the act of combining two substances that do not naturally mix. Oil and water are combined to make all sorts of food products like vinaigrette salad dressing, mayonnaise and butter. Emulsions are produced by other industries as well, including pharmaceuticals, cosmetics and chemicals.
Stable and Unstable Emulsions
Milk is a stable emulsion. It remains uniform after it is produced until it spoils. Oil and vinegar dressings are unstable emulsions. They separate after a short time and must be manually remixed. One way to create a stable emulsion is to use an emulsifier. Emulsifiers have various properties that stabilize emulsions. Examples of emulsifiers in food are egg yolks, mustard and honey. Chemical emulsifiers include sodium stearoyl lactylate and emulsifying wax.
Dispersion
Another way to combine oil and water is with dispersion, by applying a surfactant. A surfactant is a substance whose molecules are hydrophilic at one end and hydrophobic at the other. Surfactants are most commonly recognized as cleaning agents, like detergents and soaps. The molecules are able to lift dirt and grease and suspend it in water so they do not re-deposit on the surface of the thing being cleaned. Surfactants also break up oil molecules so they are evenly dispersed in the water and can be easily washed away.
Tags: combine water, stable emulsion, water combined