Oy, the Pressure on Oyster Bacteria

In pursuit of a safer oyster, Ernie Voisin and his son Mike have discovered the automatically shucked oyster.

The Voisins, officers in their family-owned seafood business, were looking for a new way to kill a sometimes dangerous strain of bacterium in raw oysters without altering the taste and texture.

After reading food-service magazines, they hit upon the process of purifying a product by using a high-strength water tank and pumps to place the food under high pressure--tens of thousands of pounds per square inch.

Aided by Dr. Marilyn B. Kilgen, head of the department of biological sciences at Nicholls State University, they tested the process on oysters at a Food and Drug Administration lab. They found that not only were the bacteria killed, but the pressure popped the shell partially open and loosened the oyster from the shell.

“It was unbelievable,” Mike Voisin said. “It produced the most perfectly shucked oyster you’ve ever seen.”

Neither the salty taste nor the texture of the oyster was affected, he said. And if the future he envisions comes true, the days of the humble oyster-shucker, who sometimes damages the oyster as he hammers and pries at the rock-like shell, may be numbered.

Not a great loss, says Voisin. While oyster-shucking is considered something of an art in Louisiana--contests are sometimes held to see who can shuck the fastest--it is not a high-paying job.

“I don’t know anyone in America who wants to grow up to be an oyster-shucker,” Voisin said.

He foresees a day when oysters will be delivered to oyster bars and restaurants with their partially opened shells held together by plastic bands that the consumer, cook or waiter can easily remove before popping the oyster open with a fork or butter knife and sliding out the meat.

But pressurizing oysters is more than a labor-saving method. More important is the pressure’s effect on Vibrio vulnificus bacteria. The bacteria thrive in warm Gulf waters and are often present in oysters, especially during summer. Harmless to most people, Vibrio can be deadly to anyone with a compromised immune system.

Reports of Vibrio-related deaths in recent years have resulted in federal rules requiring warning signs where raw oysters are consumed. Ralph Nader’s Center for Science in the Public Interest called in 1997 for a federal requirement that all oysters be heat-treated (a process commonly referred to as pasteurization, although it is a lower-temperature process than true pasteurization) before being served raw.

The heat process is used by at least one Louisiana seafood processor with some success. However, it adds to costs, and some connoisseurs complain that it alters taste and texture.

Prolonged chilling also kills Vibrio vulnificus, but some have complained about the cost of equipment. And, Voisin emphasized, keeping the oysters chilled for long periods only delays the delivery of the fresh product to market.

Another option is radiation, a process Voisin believes in but the FDA has yet to approve. And there is also a public perception problem. Some food-safety advocates are wary of radiation.

Cost may be a stumbling block to pressurization. As Voisin put it, “It’s not complicated, but it’s expensive.” However, he believes the expense can be overcome.

His company is awaiting a patent on a pressure machine. He has contacted potential builders, and it doesn’t need FDA approval, he said. He estimates his cost for a relatively small device to process 300 pounds (roughly 750 oysters) at a time at close to $500,000.

Voisin envisions lease arrangements for seafood companies that cannot afford such a large capital investment. The savings in labor at the shucking end may offset the equipment costs, he said.

He may face some skepticism in the restaurant business, though.

“My first reaction is--ugh,” said Anthony Uglesich, whose little seafood restaurant just outside the New Orleans central business district does standing-room-only business at lunchtime. One element of a freshly shucked oyster’s taste is the fluid held in the shell, he said. Processing the oyster ahead of time, especially in a manner that leaves the shell partially open, means the fluid is lost, he said.

However, Uglesich added, he would have to try a pre-shucked oyster before making a judgment.

He may get his chance soon. Voisin said plans are underway to install the oyster pressurizing device at the family business, Motivatit Seafood Inc. in Houma, by spring. He hopes to show it off when members of the Interstate Shellfish Sanitation Conference, composed of industry, state and federal officials, visit in June. If all goes according to plan, the first pressure-treated oysters could hit the market by late summer.

But even if he likes them, Uglesich said he would be in no hurry to lay off his oyster-shucker. He said he has never had a complaint of an illness from his non-processed oysters. Vibrio vulnificus is not a problem for healthy people and, Uglesich said, bacteria are rarely a problem if you are careful about where you get your oysters.

“I’m here a long time,” he said. “We haven’t had any problems.”