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How does pasteurization work?

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Quick answer

Pasteurization heats a liquid to a set temperature, holds it there long enough to kill most harmful microbes, then cools it quickly. The heat damages bacterial proteins and DNA, so pathogens like Salmonella and E. coli die, while flavour and nutrients survive better than in full boiling.

Pasteurization works by heating food or drink — like milk — to a specific temperature for a set time, then cooling it quickly. The heat kills most harmful microbes without ruining the taste, making products safer and longer-lasting.

Step by step

  1. Raw liquid is pumped through a heat exchanger and warmed toward the target temperature.
  2. It is held at that exact temperature for a fixed time, such as 72 °C for 15 seconds.
  3. The heat denatures bacterial proteins and DNA, killing most harmful microbes.
  4. The hot liquid passes a cooling section and drops quickly to about 4 °C.
  5. The chilled product is filled into sealed containers and kept refrigerated until use.

Key things to understand

  1. Liquid is heated to a precise temperature for a set time.
  2. The heat kills most harmful bacteria and microbes.
  3. It's then cooled quickly to preserve quality.
  4. It makes food safer and extends shelf life.

Labelled diagram

  1. Raw milk inlet

    Cold raw milk enters the system carrying bacteria that must be reduced.

  2. Heating section

    Hot water or steam warms the milk toward the target temperature.

  3. Holding tube

    Milk stays at 72 °C for 15 seconds, long enough to kill pathogens.

  4. Cooling section

    Cold water or chilled fluid brings the milk quickly down to about 4 °C.

  5. Filled container

    Chilled pasteurized milk is sealed and kept refrigerated until sold.

Continuous pasteurization of milk, from raw to chilled

Real-world examples

  • Most supermarket milk in Europe and North America is high-temperature short-time pasteurized at 72 °C for 15 seconds.
  • Ice cream mix is pasteurized before freezing to kill pathogens such as Salmonella that can survive in dairy.
  • Fruit juices like apple cider are pasteurized to remove E. coli O157:H7 linked to unpasteurized outbreaks.
  • Breweries pasteurize some bottled beer to stop spoilage yeasts and extend shelf life without refrigeration.

Common mistake

✗ Myth: Pasteurization makes milk completely sterile, so it can never spoil.

✓ Fact: It kills most harmful microbes but leaves some heat-resistant spoilage organisms alive. Pasteurized milk still needs refrigeration and will eventually spoil.

People also ask

How does pasteurization kill bacteria?
Heat denatures the proteins and damages the DNA of bacteria, so they can no longer function or reproduce. The temperature and holding time are chosen to kill pathogens such as Salmonella, Listeria and E. coli while leaving most flavour compounds and vitamins intact. Bacterial spores and some heat-loving microbes can survive, which is why pasteurized products still spoil eventually.
What temperature is milk pasteurized at?
The most common method, high-temperature short-time pasteurization, heats milk to 72 °C for 15 seconds. Other approved combinations include 63 °C for 30 minutes, called low-temperature long-time or batch pasteurization, and higher heat treatments for longer shelf life. All these time-and-temperature pairs are set to reduce harmful bacteria to safe levels.
Is pasteurized milk the same as sterilized milk?
No. Pasteurization kills most harmful microbes but not all, so the milk still needs refrigeration and has a limited shelf life. Sterilization uses much higher heat, often with pressure, to kill virtually all microbes and spores, allowing milk to be stored unrefrigerated for months in sealed packages. The two processes differ in temperature, duration and the resulting shelf life.
How does pasteurization work?
By heating food to a set temperature long enough to kill most harmful microbes, then cooling it fast.
Does pasteurization make food completely sterile?
No — it kills most harmful microbes but not all, which is why pasteurized milk still needs refrigeration.
Who invented pasteurization?
It's named after Louis Pasteur, who developed the process in the 1860s.

Part of the guide: Food & Kitchen Science →