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Post-Harvest Processed (PHP) Oysters








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What are post-harvest processed oysters?


After oysters are harvested, common food processing technologies may be used to reduce Vibrio bacteria in the oysters to non-detectable levels.

What are the benefits of PHP oysters?


In addition to reducing Vibrio bacteria to non-detectable levels, post-harvest processing kills spoilage bacteria, thereby extending shelf life and maintaining freshness and quality. Also, PHP oysters are either shucked or abductor muscles (which keep the shells tightly closed) are weakened, making PHP oysters much easier to shuck and prepare for eating.

How are the oysters handled?


Four technologies are currently being utilized:

  • Individual quick freezing (IQF) involves rapid freezing of half-shell oysters on trays, then adding a thin glaze of ice to seal in the natural juices before storing them frozen. Companies may also use IQF on whole oysters and shucked meats.

  • Low temperature pasteurization is a patented process whereby live oysters are placed in warm water for a certain time period and then immediately dipped in cold water to stop the cooking process. These oysters are packed for the half shell market or sent for further processing as shucked product.

  • High hydrostatic pressure is also a patented process that subjects oysters to high pressures (35,000 to 40,000 pounds per square inch) for 3 to 5 minutes to kill spoilage bacteria and reduce microorganisms including Vibrio to non-detectable levels.

  • Irradiation passes small doses of gamma rays through oysters to reduce Vibrio bacteria to non-detectable levels. The process takes only minutes, does not raise the temperature of the oysters, or make them radioactive. The U.S. Food & Drug Administration approved the use of irradiation on oysters in 2005.

How can I find PHP oysters?


Restaurants and retailers that sell PHP oysters may mention their oysters have been processed or treated to reduce Vibrio to non-detectable levels on menus or placards. If in doubt, ask.

Is it safe for high-risk consumers to eat PHP oysters raw?

Even though PHP oysters are processed to reduce Vibrio bacteria to non-detectable levels, they are still raw. Therefore, high-risk consumers (those with liver disease, cancer, diabetes, AIDS, or other conditions that weaken their immune systems) should eat them thoroughly cooked.

What else is the Gulf oyster industry doing to provide safer, better quality raw oysters?


The Gulf oyster industry increasingly evaluates and adopts solutions offered by modern technology to improve quality and safety, and extend shelf life of oysters. Other post-harvest processing technologies that have been researched for use with oysters include high pulse magnetic fields, X-rays, and value adding (i.e., smoked, char-grilled, steamed, pickled, marinated or pre-cooked convenience meals).

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Page last updated: November 5, 2017

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