To avoid contamination and mishaps while preserving food, Christina Ward, a master food preserver, stresses avoiding cookbooks published prior to 1994, as well as Internet recipes with unknown or noncredible sources.

While old cookbooks can be charming in their folksiness, “Nostalgia can make you sick,” she said. “I get calls from all over, from people who tell me something didn’t work out. I spend a lot of time troubleshooting, and when I tell them what they did wrong, they argue with me. They say, ‘I’m doing it the way my grandma did it.’

“They get so attached to tradition, but there’s so much more we know now. In the 1950s and ’60s, people covered jams and jellies with paraffin wax and thought that was enough. Pouring paraffin wax into jars doesn’t keep out 100 percent of oxygen, allowing bad pathogens to get in.”

Today’s preservationist would use a hot-water bath or pressure canner, and jars with two-part, screw-top lids.

“I say keep the tradition, just update the safety. It’s all about knowledge,” Ward said. “I don’t think a lot of people will start canning their own food, because it’s a lot of work, but the more information that gets out there the better, because it makes people more aware of how food is actually made and helps them to ask the right questions when they’re at a farmers market.”

She also advises that prolonging the life of food doesn’t mean keeping it forever, and cites 18 months as the outer limit of edibility.

“Some people claim food Grandma canned in 1983 is still good, but personally, I wouldn’t eat that. Would something that old even taste good? It’s certainly not going to retain its nutrients.”