I found an old-school technique to conquer my jam fears. Then I tried to figure out if it’s safe. (2024)

What home canning entails, in the most rudimentary of explanations, is the use of heat to create enough pressure to seal your canning jars and prevent bacteria from colonizing its contents.

Linda J. Harris, a specialist in microbial food safety at the University of California at Davis, told me, in effect, not to worry — especially when it comes to jam. As she spelled out in an email, jams are “preserved” by a combination of acid, with which most fruit is naturally endowed; sugar, innate and added; the application of heat; the formation of a vacuum; and, last but certainly not least, a seal. All work to inhibit microbial growth. The consoling thing, Harris noted, is that “traditional jam has a lot of safety built in.”

So what was standing between me and a flight of jars with handwritten “Nevertheless, She Preserved” labels on them? In two words, the hassle. I understood how important the process was; I just wasn’t sure I had the patience for it.

Then, at the end of May, I heard about a cookbook titled “Jam Bake” by pastry chef Camilla Wynne, founder of Canada’s Preservation Society.

It’s a collection of recipes for preserves and baked goods that incorporate them. And in the first few pages, I learned that she makes jams and jellies using a streamlined alternative to the Water Bath of Terror; she heats jars in a 250-degree oven for at least 20 minutes before ladling the hot, fruity lava into them. For once, instead of being overwhelmed, I thought, “Oh! I can do this!”

Still, I wondered just how safe it was. Why, when making jam, did everyone else seem so tightly bound to the water-bath method? Was it simply that it’s what the USDA and, accordingly, the National Center for Home Food Preservation, recommend?

“USDA and university recommendations are very conservative,” Harris said in her email. “They are meant to be ‘fail safe’ instructions” that account for variations in a home cook’s ingredients, equipment, experience, cleanliness and more.

In the first chapter of “Well-Preserved,” Eugenia Bone expounds on the rigmarole: “When foods in glass jars are processed in boiling water for a prescribed amount of time, the heat generated by the boiling water pushes the air out of the tissues of the foods and jar, creating a vacuum seal. It also sterilizes the food and jar.” The process kills “all the spoilers except the botulism bacterium,” she continues, but botulism “cannot thrive in a pH environment of 4.5 or less.” That’s why water-bath canning is used for higher-acid foods such as jams, and pressure canning for lower-acid foods such as non-pickled vegetables.

Moreover, botulism cases are rare. A study conducted by Carolina Lúquez, Leslie Edwards, Chelsey Griffin and Jeremy Sobel at the Centers for Disease Control and Prevention found that, between 2001 and 2017, home-canned foods accounted for 29 percent of total botulism cases. And in 2017, the CDC reported, the number of laboratory-confirmed botulism cases recorded in the United States was just 182, compared to 1.35 million annual cases of salmonella.

This might explain why there’s a history of successful jam-making that precedes and flouts the USDA’s prescribed course.

When Abby Fisher, who had previously been enslaved, published her cookbook “What Mrs. Fisher Knows About Old Southern Cooking” in 1881, she instructed readers to preserve peaches by curing them in sugar for 24 hours, removing the peaches and boiling their sugary juices, then adding the peaches back and boiling the mixture for 10 minutes. She would then cool the fruit completely before placing it into jars with its syrup and sealing the jar or sticking a cork in it. There is no reference to a water bath. That was 19 years after the USDA was established in 1862, but enslaved people in the South had been preserving food for more than two centuries prior.

Outside North America, the water-bath standard is barely recognized. When asked about it, Yvette van Boven, who spends her time between Amsterdam and West Cork in Ireland and is author of the Home Made cookbook series, responded by email: “Ehm, you COULD do that, but it’s absolutely not mandatory and quite an extra job. … It’s a bit over fussy in my opinion.”

Open-kettle canning involves boiling preserves in an uncovered pot until they reach their setting point, putting the jam into jars and allowing the jam’s heat to form the vacuum seal. Wynne turns the jars upside down to sterilize the interior of the lid.

She also sterilizes the empty jars in the oven before filling, but doesn’t believe it’s necessary to sterilize the bands or lids beforehand. In her book, she writes: “I know we used to heat them in hot water for 5 minutes, but I stopped doing that in 2013” after jar makers announced it was no longer necessary because of a redesign of the lids.

Kylee Newton, a jam maker from New Zealand based in London, teaches classes, sells her jars under the label Newton & Pott, and is the author of “The Modern Preserver” (2016) and the forthcoming “The Modern Preserver’s Kitchen” (October). And she never uses a water bath when making jam commercially. She trusts the open kettle or her version of it, which she refers to as the “heat sterilization fill” approach.

Like Wynne, Newton uses the oven to simultaneously sterilize and heat her jars right before filling them up. So does Gloria Nicol, a journalist and photographer who lives on the border between Wales and England and has just published a revised edition of her 2009 “Preserves and Pickles.” After cleaning them in hot, soapy water, rinsing and drying them, canners should “place the jars on their sides on a kitchen towel-covered shelf in the oven and heat to [225°F] for 20-30 minutes, just before using them,” she advises. But others often sterilize their jars in the dishwasher or in boiling water, sometimes far enough in advance that they’ve cooled down before the jam is added.

Guidelines from Britain’s Food Standards Agency for making jam at home don’t mention processing the jars in boiling water. But using sterilized jars is deemed essential.

Meanwhile, Cathy Barrow, the Maryland-based author of “Mrs. Wheelbarrow’s Practical Pantry,” has observed many home preservers in France skipping the sterilization step entirely and storing their jams in all manner of containers. Americans “insist on using canning jars and special lids that have to be thrown away and used only once and all that,” she said. “If you look at pictures of French preservers … and I see it in England as well, it’s old jelly jars with their old metal caps and mayonnaise jars and mustard jars.”

The open-kettle protocol was popular for home canners here until the 1980s, when it was deemed unsafe, as per the USDA’s website, because of its “high risk of contamination during processing.” According to Tracey Brigman, a clinical assistant professor of food and nutrition at the University of Georgia who is overseeing the National Center for Home Food Preservation, the method’s temperatures “are not high enough to destroy all spoilage and food poisoning organisms that may be in the food. Also, microorganisms can enter the food when it is transferred from the kettle to jar and cause spoilage.”

Like the USDA, her organization “recommends processing jams and jellies in a water bath canner,” she said via email. So do Health Canada and university extension services.

Bone sticks strictly to USDA formulas and instructions for preserving and does not feel confident in the open-kettle system. “It's not considered as safe,” she said, because it doesn’t guarantee a seal that will hold indefinitely.

But is that true? “I don’t know of any specific studies that have compared the two methods” and the resulting seal strength, Harris responded. However, she wrote, the “open-kettle method is presumed to have a higher rate of spoilage given the range of temperature profiles that individual jars would experience depending on how they were filled, whether first or last jar, etc. That variability is removed when all filled jars then go through a unified thermal process.”

As long as the seal is sound, jams can be stored in a dark, room temperature place for 12 to 18 months. But that’s just a “best by” guideline, clarifies Harris: “If the seal is good, there is no visible mold, and the jam looks, smells, and tastes fine it should be OK to eat much beyond that time frame,” she wrote.

Wynne’s sense is that North American home-canning recommendations are a prophylactic measure — to ensure the least possible chance of anything going awry. But for jams, jellies and marmalade, she said, “there’s a few different ways you can go about safely preserving, usually. … Those ones are the ones that are really hard to mess up.”

She gives 194 degrees Fahrenheit as the minimum temperature for the jam before canning to guarantee safety, saying that was what she learned at the Institute of Agri-Food Technology in Quebec in the course she took on preserving. She recalled that the minimum temperature needed was actually lower than that. And Harris confirmed: “Commercially, jams would commonly be filled at temperatures above 180/185℉.”

At 194 degrees, Wynne said, you’re assured of keeping your jam well enough above a temperature that might put it in jeopardy while you transfer it to your jars, “so no wild mold or yeast can get in there and survive, and also because the whole principle of how the jar seals is that the jam is so hot it creates a vacuum around itself, which wouldn’t be the case if you let it cool too much.”

To set, jams typically reach sea-level temperatures hotter than boiling water: of up to 220 degrees, as Harris points out, and “are usually boiled for some time before filling jars.”

Let’s not forget the other key component of Wynne’s equation — the sterilizing of the jars in the oven.

Harris isn’t a fan. As she explained, “Microorganisms are much more easily killed by ‘wet heat’ than by ‘dry heat.’ ”

Another wrinkle is that Ball, the jar company affiliated with Newell Brands, does not consider its jars oven-safe. “We always recommend that canners never sterilize, heat or process Mason jars in an oven,” Newell senior engineer Matt Cheever wrote in an email. Cheever agreed with Harris, explaining that glass is unevenly heated by “dry oven air” because the material is a “poor conductor of heat.”

That hasn’t been a concern for Wynne, or for Rachel Saunders, founder of the now-shuttered Blue Chair Jam company in Oakland, Calif., and author of its corresponding cookbooks. Saunders not only uses the open-kettle method, she doubles down on the oven. She preheats her jars in there, like Wynne, and then she puts them back in, once they’ve been filled with jam, for another 15 minutes to further sterilize them and their contents. “I know it will seal probably, regardless, but that doesn’t mean that what’s in a sealed jar is sterile.”

Again, not surprisingly, the Ball people are not on board. The dry oven heat can cause hot and cold spots in jars that could weaken them and “lead to thermal shock,” or breakage, Cheever wrote.

Wynne thinks putting the jars back in the oven is “a redundancy, just like a water bath.” But Saunders asks, “It’s so easy to do, why wouldn’t you?”

Barrow believes the jar-preheating adaptation of the open-kettle method should work as well, saying, “The worst thing that’s going to happen is that your jam is going to get moldy.”

Ah, mold.

While “there are very few microorganisms that can multiply/grow in jam” because of the low pH and low moisture, Harris said, guess what is the exception? “Molds, and to a lesser extent yeasts,” she wrote. “That is why molds are the organism of greatest concern with jam spoilage.”

In the Great Moldy Jam Debacle of 2020, Sqirl, a cafe in Los Angeles known for artisanal jams, was caught harboring (literal) buckets of the stuff covered with mold, scraping it off and swiping the jam beneath onto its beloved ricotta toast. Of course, this doesn’t sound good. But it’s not entirely uncommon. When health inspectors would visit her kitchen, “they would tell me I was a low-risk company because most of the time what can happen with preserving is mold,” Newton told me. “As much as mold is not great and people don’t like it, and they think if you’ve got mold on the top … it spoils down into the jam, I’m still of the ilk of taking the mold off the top and eating what’s underneath.”

Scientists are not as easygoing about mold. In a previous article for The Washington Post about the Sqirl hubbub, a professor of food microbiology at Cornell University’s food science department said that once you have mold on a surface, the product is tainted — you can remove the offending outbreak, but the spores will linger.

Harris agreed. Moreover, “some molds can produce mycotoxins,” she wrote, and while they don’t “usually cause acute illness like you would find with other types of foodborne illness,” they have been “linked to some forms of cancer that would develop over time.”

Though I’m not a scraper (if I see it, I’m throwing my jam in the trash), the threat of a little mold doesn’t outweigh my resistance to the thought of dealing with the water bath. So I decided to give a couple of Wynne’s recipes a try, exactly as written. I started with her Bleu Matin jam, a combination of blueberries and coffee. The whole beans are cooked along with the fruit and removed before the canning begins. You don’t taste them so much; they just draw out the tartness of the blueberries. But if, as Wynne instructs, you swirl that jam into meringues and dust them with instant espresso powder, you will be rewarded with a more pronounced coffee flavor, bitterness tempered by the berries in your preserves.

None of this was difficult. And if you’re someone who thought she’d never hear the “pop” of a seal being broken as she unscrewed the lid on a jar of jam she made herself, the pride taken in such a mundane moment is enormous. It might prompt you to do it again. If you’re still a bit squeamish, you could follow Wynne’s recipes for her preserves and apply the water-bath method for processing them.

You could also use store-bought jams to prepare her sweets; Wynne recommends flavors for each recipe. Or, you could do what my friend Ali Rosen, author of the new cookbook “Modern Freezer Meals,” sometimes does: She makes jam to store in the freezer — “the laziest version of jam,” she said. No canning necessary.