The Difference Between Pasteurization, Boiling and Distillation

You will find discussions on the internet about pasteurizing water in emergency situations. In this article I want to clear up any confusion between boiling and pasteurization, and compare both methods to distillation.

Let’s start by comparing boiling and pasteurization. While there are some similarities, they are not at all the same. They both involve heating water, but the difference is the temperature to which water is heated and the length of time it is held at a specific temperature.

Humans have been boiling substances much longer than we have been pasteurizing substances. To my knowledge, no one person has been credited with discovering the process of boiling, though many have studied it. Let’s just give credit to early man or God since there are some examples of boiling in nature. The process of pasteurization, on the other hand, is named after a famous French chemist Louis Pasteur. He did much of his research pasteurizing wine and is also famous for anthrax and much other germ-related research. Pasteur is the one most responsible for the germ theory for infectious disease.


Boiling, according to Wikipedia, is defined as “the process of heating a liquid substance until there is a rapid vaporization of a liquid.” This occurs when a liquid is heated to a specific temperature referred to its boiling point. At this temperature, the vapor pressure (tendency to evaporate) of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere to not evaporate.

When the pressure exerted on the liquid is decreased, such as is the case at higher altitudes, the boiling point is lower. Example: Water boils at a lower temperature in Denver than it does at sea level. When the pressure exerted on the liquid is increased, as is the case at lower altitudes such as in Death Valley, the boiling point is higher. In other words, the boiling point of a water and any other liquid must be defined at a specific atmospheric pressure. For standardization purposes this is usually defined as 760 millimeters of pressure on the metric barometric scale or 30.0 inches of mercury on the English barometric scale. This is referred to as standard pressure.

Water boiling in a clear glass pot.

It is quite fascinating to carefully observe the side view of water boiling. As the water warms up, tiny bubbles of steam will begin forming at the bottom of the container closest to the heat source. The size of the bubbles increases as the bubbles rise and eventually burst at the surface to release the invisible steam. Faster and faster it goes until big bubbles are forming and bursting simultaneously at the surface of the water. In other words, it is boiling! Tada!

There are actually three types of boiling. The first is called nucleate boiling, as was just described above. This is where small bubbles of vapor form at discrete points. The second type is critical heat flux boiling where the boiling surface is heated above a certain critical temperature and a film of vapor forms on the surface. Transition boiling is an intermediate, unstable form of boiling with elements of both of the two main types. The boiling point of water at sea level is 100 ° C (Celsius) or 212 ° F (Fahrenheit), but as was stated earlier, is lower with the decreased atmospheric pressure found at higher altitudes. Boiling water is a very useful method for making water sterile and therefore more potable. It does this by killing virtually every microbe that may be present.


Because the sensitivity of different micro-organisms to heat varies, it is possible to kill many but not all germs or organisms by heating water to 70° C (158 ° F) and holding it there for ten minutes. This is defined to as pasteurization of water.

The process of pasteurization does destroy some biological contaminants but it does not remove them. It also evaporates some gases and liquids with low boiling points but it, like boiling, concentrates some of the inorganic chemicals such as heavy metals and nitrates. Here is a big one—Pasteurization does virtually nothing to deal with viruses.

Pasteurization is a very useful process for substances other than water. It’s most commonly applied to milk, beer and other alcoholic beverages, vinegar, eggs, even almonds are sometimes Pasteurized as well as several other food products. Pasteurization is not guesswork however. There are specific procedures and temperatures involved for each product.

Pasteurization of water is a step in the right direction but it is simply not an adequate treatment for most tap water today. Let me explain why. Some micro-organisms are more resistant to heat and require heating for at least one minute at the boiling point of water. The destruction of viruses requires the boiling of water for at least 20 minutes! Clostridium spores can even survive this treatment, but because this infection is caused a microbe in milk and is not water-borne, this is not a water problem. (Fortunately there are antibiotics that kill clostridium spores.)

I want to mention two more significant differences between pasteurization and boiling. First—and this is a significant point—boiling is recommended by FEMA and the Red Cross for treating biologically contaminated water in an emergency while pasteurization is not. Second, from a more practical perspective, it’s much easier to tell when water is boiling than to take it through the pasteurization process.

One of the problems of both boiling and pasteurization is that while these processes can kill biological contaminants, other types of contaminants such as chemicals and metals such as lead will actually become concentrated in the boiling water. Why is this?

The steam is pure water, and it’s leaving. Which means that the water that remains in the boiling pot gets increasingly contaminated with inorganic and most organic contaminants. This brings us to distillation, because in distillation we are boiling the water and then capturing the pure steam and then cooling this steam back down into high-purity, liquid water. So, in effect, distillation is the opposite of boiling water, because the boiling water actually is what we want to throw away.

The process of distillation (assuming that the distiller is designed properly) is the single most effective water treatment process that there is. In summary, if you are only concerned with biological contaminants in water, boiling is an effective method and is definitely better than pasteurization. I recommend that you simply drop pasteurization of water from your thought process. Definitely the best process is distillation.

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