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Grades 6–8 · Everyday Life

How does pasteurization change a liquid food?

Pasteurization is a controlled treatment used to reduce harmful microorganisms in foods such as milk. During heat pasteurization, the product is heated for a specified exposure. The heating inactivates target microorganisms, meaning they can no longer grow and reproduce. The product is then cooled as part of the processing route.

J77 visual explanationControlled heating inactivates target microorganisms; temperature and exposure time both matter. The invented cell account starts with 10,000 and supplies 99 percent inactivation: 9900 inactivated and 100 remaining. This is arithmetic, not a thermal-inactivation model. Pasteurization is not sterilization; no time-temperature settings, organism resistance, safety conclusion or storage instructions are supplied.Pasteurization uses a controlled heat treatmentLiquidfoodControlledheatingProductcoolsHeat inactivates target microorganisms.Temperature and exposure time both matter.Other microorganisms can remain afterward.Process schematic; no operating settings are shown.

In the diagramPasteurization uses a controlled heat treatmentLiquidfoodControlledheatingProductcoolsHeat inactivates target microorganisms.Temperature and exposure time both matter.Other microorganisms can remain afterward.Process schematic; no operating settings are shown.

Controlled heating targets microorganisms. Temperature and exposure time both matter, and other microorganisms can remain afterward.

Temperature alone does not describe the treatment. Exposure time matters as well: a cell experiences heat over a period, rather than responding only to the highest temperature printed on a display. Different foods and processing systems use different combinations of temperature and time. Those combinations are established for the product and the organisms being targeted.

Pasteurization does not mean sterilization. Pasteurized milk can still contain microorganisms, including some that contribute to spoilage. A treatment directed at harmful bacteria is different from a claim that no living microorganisms remain. What happens after treatment also matters, because a product can become contaminated again.

Industrial processing controls help make the intended exposure consistent throughout a batch or flowing stream. The treatment applies to the product as a whole. Pasteurization therefore describes a defined process directed at target microorganisms, rather than simply a liquid becoming warm.

About this explanation

Starting knowledge: Know that microorganisms are living cells and that temperature and time are separate quantities.

Sources

  • U.S. Food and Drug Administration — Raw Milk Questions & Answers
  • U.S. Food and Drug Administration — Science and Our Food Supply: Food Safety A to Z Reference Guide
  • U.S. Food and Drug Administration — Grade A Pasteurized Milk Ordinance
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