Why Milk is White ?

In this publication, Why is Milk White? You can find the answer to your question.
Why Is Milk White ?


In this publication, Why is Milk White? You can find the answer to your question.

How is the typical color of milk formed? A closer look at the components provides the answers.

Almost ninety percent of milk is water. The fat content of cow's milk is between three and six percent, depending on the breed and diet of the cow. If you buy them in the supermarket, the natural fat content is often reduced. Other ingredients are lactose and proteins, including casein, which can be converted into cheese. Milk also contains very small amounts of various other substances such as magnesium, calcium or enzymes.

The many substances in milk make it a so-called polydisperse system. The dispersion consists of a medium (water in the case of milk) and other substances dispersed in the medium. However, milk is often referred to as an emulsion, i.e. a mixture of two liquids, not a dispersion. Because the oil floats in the surrounding water as small droplets. Immediately after milking, this emulsion is very unstable. The oil quickly settles and rises, forming a layer of cream on the surface.

Therefore, before going on sale, the milk is homogenized: the liquid is sprayed through fine nozzles onto a metal plate and breaks up the oil droplets to almost the same size. Droplets with a diameter of just a few hundred nanometers disperse better in milk. Among other things, emulsifiers, which are part of the natural components of milk, prevent them from flowing back together. They consist of molecules with a water- and fat-soluble part. They surround the droplets and separate the oil from the surrounding water.

When light falls on a liquid, some of it is reflected from the surface and the rest penetrates. Because of the many oil droplets and other substances floating in the milk, the light is highly scattered. Therefore, the milk is cloudy. Scientists call this type of scattering, which also occurs in other emulsions and dispersions, the Tyndall effect. On the other hand, if you add other substances such as salt to the water, the liquid will remain clear. Because salt ions are much smaller than the components of milk and are more evenly distributed in water. This creates a solution in which light is hardly dispersed.

Milk appears white to us because the oil droplets in it scatter all wavelengths of visible light countless times. And because sunlight or, for example, light from an incandescent lamp covers the entire visible color spectrum, from red to yellow, green and blue to violet, these colors mix and the impression of white is formed.

An interesting effect is created by pouring a few drops of milk into a tall glass of water, holding a flashlight from above. If you look at the glass from the side of the flashlight beam you will see a bluish glow, if you look down the mixture looks reddish. The reason: the light that fell completely through the glass and re-emerged at the end followed a further path than the light reflected from the side.

Blue, short-wave components scatter more in the longer path than long-wave, red components. Therefore, the blue color appears in the center of the glass, while the red light can penetrate most of the liquid. Air molecules scatter light similarly, so in the morning or evening when the sun's rays are sideways in the atmosphere, the sky appears red. However, so much substance floats in undiluted milk that the effect is canceled by frequent refraction of light.

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