Whether it’s with your cereal first thing in the morning, or in a glass with some chocolate syrup at night, milk is a staple part of most people’s diets. If it’s anything like mine, your family probably goes through at least a few gallons of milk every week, if not more. Milk comes in all different forms, too: without milk, you wouldn’t be able to put that whipped cream on your apple pie, or butter your toast during breakfast. Although it seems pretty simple, the physical status of milk is actually extremely complex, especially when it comes to the chemistry behind it.
The Chemistry Behind Milk
If you were to leave a glass of milk to sit for some time on your countertop, you would begin to see a thin layer of cream form on the surface of the milk. What exactly is this? Well, if you were to view this layer under a microscope, you would see shapes floating around in the milk, which is the fat. In chemistry, this is known as an emulsion; specifically, an emulsion of fat in water. An emulsion is a mixture of two or more liquids that are non-mixable. If you were to shake the glass of milk, the emulsion would be broken down and the milk would go back to normal. However, milk does come in more than one form, such as butter – the difference is that butter is an emulsion of water in fat. So when the milk is churned into butter, there is a phase change that is involved in the process.
The fats that are present in milk are there for a reason- they act as a solvent for all of the fat-soluble vitamins in milk that make it so healthy, such as Vitamins A, D, E, and K. In the milk fats, the fatty acid molecules are made up of a hydrocarbon chain along with a carboxyl group, or COOH group, usually, consisting of all single bonds, one double bond, and an even number of carbon atoms. Structurally, these chemical molecules look something like this:
Other properties of milk, such as the melting point and the hardness of the fatty acid, is affected by various factors such as the length of the previously mentioned carbon chain as well as the degree of unsaturation (when a molecule is unsaturated, this means that it does not have the greatest possible amount of hydrogen atoms that it can have for the number of carbon atoms that it has. In other words, fats with a lot of these high-melting fatty acids will be hard; but fats with a high content of low-melting fatty acids can make the spreadable butter that you put on your toast every morning.
Making Your Milk Taste Its Best
Depending on what kind of environment your store your milk in, you may notice that the milk tastes different. Changes in storage can cause different types of chemical changes to occur in the milk, one of them being oxidation. Although most people tend to think that milk changes or goes bad when it is left outside of a refrigerator because of the higher temperatures, there are actually a lot of chemical processes occurring in milk when it is exposed to lower temperatures as well, such as the oxidation of the fats in the milk.
Although the oxidation of the fats in the milk can be counteracted by reducing agents that are present in the milk, such as lactic acid bacteria, there are still many chemical changes that may cause some unwanted things to occur in your milk. For example, chemical change that occurs due to the oxidation of the fats in the milk is the “flavor” of the milk – although plain milk does not actually have a flavor to it, lower storage temperatures usually cause milk to develop an unpleasant flavor. This is why companies that produce milk place great emphasis on precise refrigeration for their milk, because nobody wants their milk tasting funky!
Among the many beverages that have come to prominence in society throughout history, milk, along with water, is probably among those that will continue to be a mainstay in the diets of people both young and old. The small cardboard milk carton you get at lunch, the glass full of milk that you dip your Oreo in, the milk mustache you get on your upper lip when you take a sip. All of these are iconic images that come to mind when one thinks about milk throughout history. After taking away this information regarding the chemistry behind milk, one could also realize that not only will milk remain a staying force forever, but so will its chemistry.