Post-Harvest Processes

Gulf Coast oyster processors have taken the lead in developing new technologies to ensure safer alternatives to traditional raw oysters for at-risk consumers. These processes allow the oyster to be consumed raw, but with added safety features that reduce Vibrio vulnificus to non-detectable levels. At-Risk oyster consumers can now eat raw oysters with reduced risk of Vibrio vulnificus illness.

Three post-harvest treatment processes currently exist on a commercial scale(1): individual quick-freezing (IQF), low heat pasteurization or heat-cool pasteurization (HCP), and high-hydrostatic pressure (HPP). Although these technologies currently account for less than 10% of all oyster sales in the United States, on-going marketing and educational efforts geared toward the at-risk consumer are expanding acceptance and knowledge regarding these oyster products.

Each process has unique advantages and characteristics which provide greater convenience for all customers, while at the same time reducing risk for at-risk consumers.

IQF - Freezing oysters to extend shelf life was first applied in 1989; and presently, there are several facilities using this technique with oysters. The process has also become popularized on a worldwide scale with Australia, Canada, New Zealand and the United States leading the pack. IQF processing of oysters is presently being applied by companies in California, Florida, Louisana and Texas. It has the biggest market share of the post-harvest processed raw oyster market. Many prefer the IQF oysters because of quality, taste, and convenience. The IQF “fresh frozen” technology keeps all of the flavor and appeal of non-processed oysters – the major selling point of the process. IQF oysters are typically sold with the top shell removed.

HCP - Heat-cool pasteurization of oysters was initially developed in 1995 by a private firm in Louisiana. This process involves submerging the raw product into warm water followed by immediate cold water immersion. Shellstock is washed, graded, sorted, banded and treated. Banded oysters are placed on a large tray and then a hoist lifts and places them in warm water at 127oF for 24 minutes. The trays are lifted out and placed in 40oF water for 15 minutes. The trays of cooled, banded oysters are stacked on carts to drip dry ready for boxing and storage.

HHP – High pressurization processing was pioneered in the meat and juice industries; however, its application to oysters was initiated in 1999 in Houma, LA. This type of processing starts with cleaning, washing, sorting and grading oysters. They are then banded and containerized (placed in a stainless steel cylinder) in preparation for the high-hydrostatic pressure of 45,000 pounds per square inch. After pressurization, the oysters are then shucked for half shell or packaged as banded oysters.