MadSci Network: Engineering

Re: Are gamma or UV rays used to sterilize milk stored at room temperature?

Date: Tue Jul 4 07:39:48 2000
Posted By: Edward Peterson, Staff, Chemical Engineering, S&B Engineers and Constructors
Area of science: Engineering
ID: 957400330.Eg

Dear Judy,
I worked with a company in Sweden that packages milk and other liquid products named Tetra Pak. You can often find their name on the bottom of cartons of milk or fruit juice that is stored at room temperature.

When I worked for them, they did not use UV or gamma radiation to sterilize milk. If you visit their web site, you can find good information to explain the paste urization and packa ging processes to you, but in short, here goes:

First, they heat the milk to very high temperatures for a short time. This tends to reduce the milk flavor, but kills many more bacteria than in normal U.S. processing. Second, the packaging has a thin metal layer that prevents oxygen from getting into the package. Without oxygen, micro-organisms have difficulty propagating. The packaging technique prevents air from being in the package when the package is sealed in the first place. Therfore, there is very little air (oxygen) for bacterial growth to begin with. The package is actually very complex and includes polymer barriers to adhere the aluminum metal barrier to the polymer structure that keeps the liquid from getting out, and then a layer of polymer that sticks the paper to the polymer.

Unusual energy technology is used to seal the packages! They employ low frequency induction sealing to heat the aluminum directly in the package structure that then melts the polymer inside layer. That happens in about one-half second.

Dr. Ed Peterson

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