CORVALLIS - The Oregon State University Extension Service has issued a food safety warning for home canning of tuna.
Calls to the OSU Extension food preservation hotline indicate that many people are using the wrong canning method and exposing themselves to the risk of botulism, a deadly food poisoning.
"You must use a pressure canner, not the water-bath method, to process tuna and other low acid foods, such as vegetables," said Carolyn Raab, OSU Extension foods and nutrition specialist.
Only a pressure canner reaches the high temperatures necessary to kill the bacteria that cause botulism. Botulism is a paralytic illness that begins with blurred vision, slurred speech, difficulty with walking and swallowing. It eventually paralyzes the entire body.
Unless there is prompt treatment with an antidote, death may result.
Home canners also need to be sure their pressure canner is in good working condition. "Replace the gasket if it isn't in good condition and obtain operating instructions if you've lost them," Raab said.
If the pressure canner has a dial gauge, the gauge should be checked for accuracy each year. Contact the county office of the OSU Extension Service for information on where to have dial gauges checked locally.
Up-to-date canning instructions are essential. The instructions in canning manuals published before 1988, the year the U.S. Department of Agriculture made major changes in home canning instructions, are outdated and should not be used, Raab pointed out.
"If you use Ball or Kerr manuals, look for a copyright after 1988. A lot of pre-1988 canning books are still on kitchen shelves where they continue to pose a threat to health," Raab said.
Raab gave the following guidelines for canning tuna:
- Tuna may be precooked or raw. Precooking removes most of the oil that tends to be strong-flavored. However, many people find it easier to can tuna raw in its own juices.
- Use half-pint or pint canning jars and lids. About one pound of fish will fill a half-pint jar. After preparing and packing the fish, process it for 100 minutes. You might want to process outside on a camp stove to prevent indoor odors.
- At sea level, use 10 pounds pressure for a weighted gauge canner or 11 pounds for a dial gauge. Pressure must be increased at altitudes above 1,000 feet for a weighted gauge canner and 2,000 feet with a dial gauge canner. Pressure corrections are listed in canning manuals.
- Before starting the timing, let steam escape for 10 minutes to remove any cold spots. Then close the petcock and bring the canner up to pressure. Maintain the canner at the correct pressure by watching the dial gauge or monitoring the jiggling of the weighted gauge.
"Watch the canner closely the whole time. If the pressure falls too low, you'll need to start timing all over," Raab said.
Several OSU Extension Service publications can help you preserve your tuna: "Using and Caring for Your Pressure Canner," publication PNW 421, $1 per copy; "Canning Seafood," publication PNW 194, $1 per copy; and "Home Freezing of Seafood," publication EC 1363, 50 cents per copy. Copies of these and other publications can be obtained at county offices of the OSU Extension Service.
They are also available by mail. Send your request and check or money order payable to OSU to Publication Orders, Extension and Station Communications, OSU, 422 Kerr Administration, Corvallis, OR 97331-2119.
"Canning Seafood" and "Home Freezing of Seafood" are available on the World Wide Web at eesc.orst.edu. Click on "Publications and Videos," then "Family and Home" and "Food Preservation and Storage."
For assistance with specific tuna preservation questions, call the OSU Extension Service's Food Preservation Hotline (1-800-354-7319) which operates from 9 a.m. to 4 p.m. weekdays until Oct. 15.