Finding the Cause of “Soft” Caviar

December 18, 2007

Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334

To the dismay of the nation’s largest cultured white caviar farm, the quality of its caviar has slipped in the last two years due to an unexplained rise in the incidence of soft-egg syndrome.

To help an otherwise growing farmed caviar industry, one that is praised by some environmentalists as offering consumers an environmentally friendly alternative to wild caviar from the depleted Caspian Sea region, California Sea Grant will soon be funding a research project to identify the causes of soft sturgeon roe at Stolt Sea Farm in Sacramento. The hunch is that the sturgeons’ diet is to blame.

Farmed white sturgeon caviar has become a popular alternative to wild-caught specialty caviars from the Caspian Sea region. The severe depletion of wild stocks is increasing demand for farmed caviar. Photo: Stolt Sea Farm.

The project is being led by researchers in the Department of Animal Science at the University of California at Davis in collaboration with UC Cooperative Extension and Stolt Sea Farm.

“The goal of the project is for us to hit much higher and tighter markets,” said Stolt’s manager Peter Struffennegger.

Caviar is graded on four characteristics: color, taste, size and texture. “Most chefs have different ranking as to the importance of the various characteristics,” he said. “If you don’t hit one of those characteristics, you lock yourself out of that market.”

As the name suggests, caviar with soft-egg syndrome is soft. “Soft-egg syndrome means the texture is losing,” said the project’s leader Kenji Murata, a biochemist at UC Davis. “We cannot sell soft eggs as first-grade products. We have to sell them as a lower-grade product, maybe as a C-grade.”

If only a small percentage of eggs had the syndrome, it would be a manageable loss for the farm, but as much as 20 percent of eggs are being affected, Murata said.

“We don’t know what is causing soft eggs,” Stuffennegger said. “Our feeling is that it is diet,” because nothing else has obviously changed in the last two years when the syndrome started becoming a serious problem.

“We know it is not our processing techniques,” he said, “because the eggs are soft going into the tin. We

White sturgeon, above, can reach gargantuan proportions, though today such large catches are extremely uncommon. Photo Credit: Silas Hung, UC Davis.

have photos of eggs cracking. You add salt and the salt reacts with the egg and the egg becomes even softer.”

He also does not think the soft eggs are due to stress caused by handling and transport, though both will be studied.

The feed is the primary suspect since it is the one aspect of husbandry the farm does not completely control because feed recipes are proprietary. The balance of fishmeal to vegetable protein could have changed slightly, Struffennegger said, or the quality of fishmeal could be lower or deficient in some micronutrient due to changes in wild fisheries off Chile and Peru. “We just don’t know.”

Given the farm’s hunch that diet is at the root of the problem, the Sea Grant project will focus on how diet affects egg burst force and other more technical egg qualities such as the incidence of ovarian follicular atresia, the degeneration of the egg folicule, at harvest. The scientists will also examine whether stress, through handling and transport, can trigger soft egg syndrome. Water temperature is another key environmental factor that will be explored.

“There are a lot of smoking guns,” Struffennegger said. “It is about finding out what direction the bullet is coming from.”