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For many meat eaters the proof is in the pink. They use the meat's color as a guideline to determine the food's freshness. But, many meat manufacturers actually inject the food with carbon monoxide to give it that fresh, reddish-pink look. The carbon monoxide binds with a pigment in the meat and keeps the colors vibrant and red.
Japan and Canada along with many other countries in Europe, have banned the use of carbon monoxide in meat. The US Congress is debating whether the producers should be allowed to continue the process in the United States.
Consumers who are unsure whether their grocery store allows carbon monoxide-treated meat and no longer want to use color as a freshness indicator do have other, safer options.
They should look for the freshness date. The meat also should feel springy to the touch and
the fat should be white, not yellow in color.Finally, the best sign of spoiled meat happens once the package is opened. Spoiled meat smells bad and has a slimy texture.
http://abcnews.go.com/GMA/Consumer/story?id=3863064&page=1