food canning

Bottles of food sit on a kitchen shelf in this 2010 file photo.

Editor’s note: This story is a part of a short series on home canning safety.

Electric pressure cookers, such as the Instapot, may be the first kitchen gadget since the 1940s as ubiquitous and enduring as the microwave oven, but the USDA and university extension centers across the United States have major concerns about manufacturer claims of being safe enough for pressure canning to prevent life-threatening botulism — especially at Utah’s altitudes.

Utah State University Utah County Extension Assistant Professor and team leader Cathy Merrill, along with five other USU Extension faculty, obtained a grant and recently completed the first preliminary study on electric pressure canning safety. The results support their concerns which they will present to the National Extension Association of Family and Consumer Sciences Convention this October in Hershey, Pennsylvania. They are also hoping to publish their findings in The Journal of Extension.

Soon after Merrill was hired in January of 2017, she received a call from a pregnant mother who had put up 90 pints of pureed peas, wondering if the peas would be safe to feed her baby. Merrill began researching and what she found was disturbing.

“Power Pressure Excel, for example,” Merrill said, “claimed ‘We are made for canning.’ But if you look in the small print, it tells you not to use at over 2,000 feet — meaning that they have used it at sea level and feel it’s safe at sea level. We don’t have sea level in Utah! And how many people always look at the fine print?”

Merrill tried calling one of the international companies that manufacture pressure cookers to find out what research and experimentation had been done to ensure safety.

“When I asked if they had done testing on low-acid foods or done any pH testing,” Merrill said, “they responded with, ‘What is pH?’ That could just be a language barrier, but it really scared me. … The University of Georgia, which is our flagship center and who also put out the USDA’s Complete Home Canning Guide, has been contacting manufacturers and asking them what they are doing to test their cookers, and the manufacturers have been blowing them off.”

Extension centers just can’t tell people that electric pressure cookers are safe for canning if good research hasn’t been done, Merrill said.

“Many of the manufacturer instructions for these electric canners tell people to go to the USDA website for times for canning,” Merrill said. “They were using our times, but we just don’t know that those times are safe for smart cookers. They didn’t put that part in their instructions.”

Extension centers are about sharing reliable information, so the “Complete Home Canning Guide” from USDA and University of Georgia is backed up by solid research: “microbial challenges, multiple replications, data logs, etc.,” Merril said. “The manufacturers of these canners have not shared with the USDA what research they’ve done — if they’ve done any research.”

Merrill said that previous studies on these cookers had shown that at different altitudes, the cooking times of regular recipes associated with the cookers needed to be adjusted, but nobody had done any research on how altitude affected the time of safety for canning. Merrill explained that the higher the altitude of a location, the more pressure is needed to raise temperatures to 250 degrees Fahrenheit — the thermal death point for Clostridium botulinum spores in conventional low-acid pressure canners.

Merrill, with the help of other USU Extension faculty members Karen Allen in Logan, Susan Haws in Summit County, Teresa Hunsaker in Weber County, Tricia Mathis in Wasatch County, Ellen Serfustini in Carbon County, and Paige Ray in San Juan County, have now completed the preliminary research to make sure these cookers could reach and hold the necessary temperature to ensure safety.

Merrill explained that the botulism bacteria have protein-coated spores that are very difficult to denature. The spores are everywhere but do not pose a problem in high-acid, high-oxygen, low-moisture or low-temperature conditions, so freezing and dehydrating foods such as vegetables and meats is just fine. But canning provides the perfect low-acid, low-oxygen, high-moisture and room-temperature conditions to produce the colorless, odorless botulism toxin if not eliminated.

The research team tested three electric pressure cookers: the Carey, Power Pressure Excel, and Instapot at three different altitudes in Utah: Monticello at 7,000 feet, Provo at 4500 feet (the same altitude as Cache Valley) and St. George at 2,900 ft. They used three different foods: raw packed green beans, hot-packed pinto beans, and hot-packed chicken. Raw-packed foods require longer times because they have to be cooked as well as canned. Hot-packed foods have already been cooked. They put data loggers inside each jar that recorded magnitude and hold of temperatures reached.

The results? Only one of the cookers — the Carey — reached 250-degrees at two of the sites. And even then, at one of the sites, it didn’t reach it for the length of time required for green beans. The other two cookers never reached the required temperature at any altitude.

“This is just a preliminary study,” Merrill said. “We still don’t know even if it reaches temperature if it’s safe. We didn’t do a microbial challenge study where they inoculate the food so they know exactly how many spores it contains before and after experimentation.”

Merrill also explained that with stovetop conventional pressure canners, “you do a natural release and wait to open up until the cooker has come down off of pressure by itself … up to 30-40% of the microbial death is during that cool-down. The cookers like Power Pressure Excel don’t have a cool-down cycle.”

Though Merrill would not can with her electric pressure cooker, she loves using it for regular cooking and, having raised 10 children and canned throughout those years, looks forward to the day she can safely use one for canning.

“It would be nice to push a button and walk away,” Merrill said, “and not have to diligently babysit the pressure gauge on my conventional canner to make sure it stays at pressure.”

Merrill also sees the electric canners becoming even more relevant in the future to the more modern health-conscious small-garden growers.

“The trend is healthier foods, and you get healthier foods by doing it yourself,” Merrill said. “I think they’ll come up with something that works. They just haven’t yet.”

More information about food processing can be found at extension.usu.edu/canning. Merrill also said that local Extension centers are always happy to take calls.