What Is the Difference Between Pasteurized and UHT Milk? Pasteurization, like any other technology, has progressed, resulting in new approaches, new results, and increased food safety.

However, the distinction is not always evident. Isn’t all of the milk we drink pasteurized? What does the abbreviation UHT stand for? How do they differ from natural, pasteurized, and unpasteurized milk in flavor and nutrition?

How long will these keep in the fridge? What about outside? All of these inquiries will be addressed.



In the mid-1800s, a clergyman compelled to “learn” by his father discovered that heating milk before bottling extended its shelf life. The technique developed as a result of this experience resulted in liters upon liters of safer milk for human consumption.

Today, in Spain, we call pasteurized milk that has been subjected to the process of pasteurization, which consists of heat below 100 °C for a moderate period of time to improve safety and preservation.

We’ve already seen that this is the method for heating milk below 100 degrees Celsius. On a technical level, as with UHT, we distinguish between two more or fewer standard techniques in Spain:

  • Heat at 63 ºC for 30 minutes, which is “classic” pasteurization.
  • Heat to 72 oC for about 15-20 seconds, or HTST, from English high-temperature short-time flash pasteurization.

Which of these two strategies should you use? The main difference is that the second takes far less time, uses fewer resources (such as energy), and respects milk qualities such as taste, fragrance, and composition better. For this reason, almost all pasteurized milk on the market today is HTST.

Although pasteurization is quite effective at removing bacteria that might cause severe food poisoning in milk, sterilization is not achievable, and the microorganisms are exceedingly persistent. Even if you destroy their “living” forms, they have a “resistance” form that is similar to spores.

When they are exposed to heat, or the environment becomes toxic, or the environment becomes desert, the microorganisms become lazy and wait for a better opportunity to grow again and continue to survive.

Sterilization also eliminates various types of resistance, preventing milk from deteriorating or causing health issues. And how can this be accomplished if pasteurization is insufficient?


UPerized, ultra-pasteurized, or UHT milk (from ultra-high temperature), It is an evolution of pasteurization. In this process, they reach between 110 and 150 oC for different time periods.

However, heating the milk to this point can cause it to lose flavor, color, smell, or nutritional properties (or turn it into something else entirely). What is the solution to this? Heat it for such a short period of time that none of the above happens. Thus, there are two processes:

  • The heat is between 110 and 120 oC for 15-20 minutes.
  • The heat is between 135 and 150 oC for 2 to 8 seconds.

The first, although at a lower temperature, takes advantage of the time to sterilize the product. Yes, this procedure can kill pathogens commonly present in milk, even in their resistant forms.

This is done in closed and isolated circuits to avoid any external contamination. eye, because this disinfection is called “comsterilization,” but it is not total sterilization.

To eliminate all the organisms that live in products like milk would require much more aggressive treatments, which would completely ruin them.

What Is the Difference Between Pasteurized and UHT Milk?
For the moment, this commercial sterilization is good for us because it kills all the microbes that can cause the loss of properties or certain diseases in human beings.

Therefore, UHT is the type of milk found in tetra-brick, the most commonly consumed.

What Is the Difference Between Pasteurized and UHT Milk?

The most obvious distinction between UHT milk and pasteurized milk is that the former is sterilized (commercially), whereas the latter is not, as you may have guessed, which affects its shelf life.

Another significant difference is its taste and scent; some people like the stronger taste and smell of pasteurized milk.

Another feature that distinguishes them is their storage: during the UHT process, the milk is automatically packaged in sterile tetra bricks, which take up less space and are easier to carry.


The first and most obvious difference, as we have seen, is due to the temperature of the sterilizing process: although pasteurized milk can not reach 100°C, UHT milk can much exceed it. The ramifications lead to another major difference: its length.

As previously stated, pasteurized milk kills bacteria that provide an immediate threat but not their resistant variants, which allows them to recuperate. To postpone its “return” to life, pasteurized milk is kept cold from the outset and has a four-day shelf life from the time it is packaged.

On the other hand, UHT can be stored at room temperature for months after commercial sterilization and adequate packaging because there is no need to be concerned about delaying the most active microorganisms because they have been removed.

It should be kept cold once opened, even though its shelf life can be greater than pasteurized milk, depending on the contamination it acquires when exposed.


Another distinction is storage: after UHT processing, the milk is automatically packaged in sterile tetra bricks that take up less space and are easier to carry.

This, paired with its long shelf life, enables significantly greater transport than pasteurized milk, which is often stored in stiff, cold-proof containers (not always, of course).

As previously stated, there is a significant variation in the length of these two types of milk. is administered from the beginning of pasteurization to avoid giving rise to bacteria returning from their spores. Microbes, like humans, have preferred temperatures.

When their environment (such as our milk) slips outside of this range, they have difficulties feeding, bonding, and reproducing.

Even if they did not die, as we have seen, keeping it cool makes it more difficult for them to multiply and risk the milk’s preservation.

On the contrary, UHT does not suffer from the advent of undesired bacteria because it has removed the spores of these organisms (at least the most frequent). At least not initially.

Bottle and glass of milkAs previously stated, commercial sterilization is not complete sterilization. The reason is that eliminating all organisms without damaging the milk is difficult.

That is why it can linger for months, but not indefinitely. However, as soon as it is opened, the microorganisms that float in the air (yep, we are surrounded) will contaminate the milk.

This is why it is critical to place it in the refrigerator, where it might last for a longer or shorter period of time depending on the number of germs that have found their way there.


Another significant change that has increased the use of pasteurized milk is its taste and scent. We can distinguish between organoleptic characteristics (from the Greek organoleptic, which is sensed by the senses).

Pasteurized milk, while more difficult to store and transport (and thus more expensive), is experiencing an exciting surge due to its greater flavor and fragrance.

We also stated that this is related to the process. With a lower temperature, pasteurization induces fewer changes in the molecules and chemicals that make milk what it is.

As a result, some people prefer the taste and aroma that is stronger and more similar to milk in its “original” state.

If we heat the milk for a long time, we can spoil its proteins or caramelize the lactose (this is how we obtain dulce de leche, for example), so the more minutes it takes to heat, the more the milk ceases to be milk.

Although in just a few seconds, many of these processes do not occur (in significant quantities), it is true that the difference is noticeable, as shown by PD tests on consumers around the world.

The issue of fat is less evident, as it eventually undergoes its own alteration due to the availability of skimmed, semi-skimmed, and whole milk.

However, there are differences between pasteurized milk and UHT, albeit this is dependent on the brand and technique used. Is this to say that pasteurized milk is superior? I wouldn’t dare say that. And, as they say, colors are solely for the eyes.

Are there differences in nutritional properties between pasteurized and UHT milk?

One question remains unanswered: is there a nutritional difference between these two forms of milk?

If we say that heat alters its qualities, and thus the process occurs in very short bursts of time, it is logical to suppose that its worth as food will change as well.

However, we have no scientific data to back this up. According to the studies and analyses that have been published to date, the two are nutritionally equal.

This is attributable not only to the nature of milk as a material but also to the way our bodies ingest nutrients. However, in the end, there is no distinction.


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