Ultra-high-temperature processing facts for kids
UHT processing (which stands for Ultra-High Temperature) is a special way to treat liquid foods. It heats them to a very high temperature, about 140°C (284°F), for just 2 to 5 seconds. This super-fast heating kills all harmful bacteria and their tough spores. UHT is most often used for milk. But it also works for fruit juices, cream, soy milk, and even soups! UHT milk first became available in the 1970s.
The high heat can sometimes change the taste or smell of dairy products a little. Another way to treat milk is flash pasteurization. This heats milk to 72°C (161°F) for at least 15 seconds.
UHT milk is packaged in special sterile containers. This allows it to stay fresh for six to nine months without needing a refrigerator! Regular flash-pasteurized milk, however, only lasts about two weeks in the fridge.
Contents
How UHT Milk Started
People have always used heat to make milk safe and last longer. The first system to heat milk continuously was made in 1893. It heated milk indirectly. In 1912, a method was invented to mix steam directly with milk. This heated it to very high temperatures, around 130°C to 140°C (266°F to 284°F).
However, there was a problem. There were no special packages to keep the milk sterile after heating. So, these early ideas didn't become popular until the 1950s. In 1953, a company called APV created a new way to inject steam into milk. They called it Uperiser. This heated the milk instantly. The milk was then put into sterile cans.
Tetra Pak's Role
In Sweden, a company called Tetra Pak started making special paper cartons in 1952. These cartons were shaped like pyramids. In the 1960s, Tetra Pak made a big breakthrough. They combined their cartons with a new way to package food. This was called aseptic packaging.
Aseptic processing is very clever. The food and its package are sterilized separately. Then, they are put together in a super clean, sterile room. This is different from canning. In canning, the food is put in the can first. Then, both are heated together. Tetra Pak's new method helped UHT milk become popular around the world.
UHT Milk in Different Countries
In 1993, a company called Parmalat brought UHT milk to the United States. Many American shoppers were not used to buying milk that wasn't refrigerated. So, Parmalat started selling UHT milk in regular-looking cartons. They even put it in the refrigerated section of stores. This helped people feel more comfortable buying it.
In 2008, the UK government thought about making most milk UHT. They believed it would reduce the need for refrigeration. This would help the environment by cutting down on greenhouse gas emissions. But the milk industry didn't agree. So, the idea was stopped.
How UHT Processing Works
UHT processing happens in big, complex factories. These factories have many steps that happen automatically.
- Flash heating: The liquid is heated very quickly.
- Flash cooling: The liquid is cooled down very fast.
- Homogenization: This step is mainly for milk.
- Aseptic packaging: The product is put into sterile containers.
In the heating part, the liquid is first warmed up. For milk, it's heated to about 70–80°C (158–176°F). Then, it's heated very quickly to the final high temperature. There are two main ways to heat the liquid: direct and indirect.
Direct Heating Methods
Direct heating systems are good because the product is at a high temperature for a very short time. This helps protect sensitive foods like milk from too much heat damage.
- Injection-based: Hot, high-pressure steam is shot directly into the liquid. This heats and cools the liquid very fast. But it only works for some products. Sometimes, the hot nozzle can make parts of the product too hot.
- Infusion-based: The liquid is sprayed into a chamber filled with steam. This creates a large surface area for contact. This method heats and cools almost instantly. It also spreads the heat evenly. This avoids any parts getting too hot. It works for both thin and thick liquids.
Indirect Heating Methods
In indirect systems, the liquid is heated by a solid surface. This surface is called a heat exchanger. It's similar to what's used for pasteurization. But since UHT uses higher temperatures, higher pressures are needed. This stops the liquid from boiling. There are three types of heat exchangers:
- Plate exchangers
- Tubular exchangers
- Scraped-surface exchangers
To make these systems more efficient, hot water or steam heats the exchangers. There are also units that reuse the heat. This saves energy.
Flash Cooling
After heating, the super-hot liquid goes into a special tube. Then it moves to a vacuum chamber. Here, it suddenly loses its heat and turns into vapor. This process is called flash cooling. It helps prevent heat damage. It also stops any heat-loving microbes from growing. Flash cooling also removes extra water from the steam contact. It can also get rid of bad-smelling compounds. The amount of cooling and water removed depends on the vacuum level. This must be set very carefully.
Homogenization for Milk
Homogenization is a step just for milk. It's a mechanical process. It breaks down the tiny fat droplets in milk. This makes them smaller and more numerous. This stops the cream from separating and rising to the top. It also makes the milk smoother and tastier.
UHT Milk Around the World
UHT milk is very popular in many parts of Europe. In some countries, like Spain, 7 out of 10 people drink it regularly. This is because it's expensive to transport refrigerated milk in warm climates. Also, cool cabinets in stores might not be very efficient.
However, UHT milk is less popular in Northern Europe. Countries like Denmark, Finland, Norway, Sweden, the UK, and Ireland prefer fresh pasteurized milk. It's also not as popular in Greece.
In the United States, most regular milk is pasteurized. But a lot of organic milk sold in the US is UHT treated. This is because organic milk often travels longer distances. UHT helps it stay fresh during shipping.
| Country | percent |
|---|---|
 Austria |
20.3 |
 Belgium |
96.7 |
 Croatia |
73 |
 Czech Republic |
71.4 |
 Denmark |
0.0 |
 Finland |
2.4 |
 France |
95.5 |
 Germany |
66.1 |
 Greece |
0.9 |
 Hungary |
35.1 |
 Ireland |
2.1 |
 Italy |
49.8 |
 Netherlands |
20.2 |
 Norway |
5.3 |
 Poland |
48.6 |
 Portugal |
92.9 |
 Slovakia |
35.5 |
 Spain |
95.7 |
 Sweden |
5.5 |
 Switzerland |
62.8 |
 Turkey |
53.1 |
 United Kingdom |
8.4 |
What About Nutrition?
UHT milk has the same amount of calories and calcium as regular pasteurized milk. However, some vitamins can be slightly reduced in UHT milk. These include vitamin B12, vitamin C, and thiamin. For example, UHT milk has about 1 microgram of folate per 100 grams. Pasteurized milk has about 9 micrograms.
The way proteins are structured in UHT milk is a bit different. This means it doesn't work as well for making cheese.
Images for kids
-
This image shows a shelf-stable UHT milk carton on the right.
See also
- Aseptic processing
- Food preservation
- Food storage
- Food packaging
- Food engineering
- Pasteurization
- Flash pasteurization
