How to Can Jam

If you're a jamateur, here's what you need to know.

If there's a downside to summer fruits, it's that their season is fleeting. Sure, modern agriculture has guaranteed that you can find berries and stone fruit during cooler seasons, but if you've ever had fresh peaches or strawberries from the farm or farmers' market, you know that supermarket fruit just isn't the same. The solution, of course, is simple: Save some of summer's bounty for later. If you're looking for a way to preserve fruit that'll also survive a power outage, then canning is the way to go. The sticky, tangy-sweet jams these fruits yield doesn't just help you enjoy the taste of summertime out of season, but also provides some light and warmth during colder, darker days. In other words, the best way to perk up a winter breakfast is by breaking out the summer's jam.

So how does canning work?

The whole idea behind canning food is making it last longer without the use of refrigeration. Instead, the food is altered chemically so that it stunts bacterial growth, and then sealed with the power of physics. Chemically, you'd alter the food by making it more acidic with ingredients such as vinegar, lemon juice, or sugar. Jams typically involve at least two of these ingredients (if you're out of lemon juice, in fact, vinegar is the best canning substitute since they have a similar pH level), making them a natural fit for the canning process. Physically, you'll either create pressure with boiling water or a pressure canner, which will keep the lids in place — and, done correctly, any possible contaminants out.

Can I make jam without sugar?

Jam isn't just sweet for taste-based reasons. Sugar helps jam achieve its trademark texture and inhibits microbial growth, which in turn helps the jam last longer. Along with acid and pectin, a heteropolysaccharide that's found in the cell walls of fruits and vegetables, sugar gives jams and jellies their semisolid texture. So sugar-free jams will have a more liquid texture unless they're supplemented with extra pectin or a thickening agent such as gelatin. They also won't preserve as well, meaning that depending on the recipe, you'll need to forgo processing the jam altogether, refrigerate the finished product, eat your jam within a few weeks, or all of the above.

That being said, it is possible to make jam with less sugar. But sugar's role will have to be met through another ingredient, whether it's sweetened pectin, artificial sugar, or gelatin. Additionally, since you're working with fruit, the jam won't be truly sugar-free. It's more accurately described as "no sugar added," since even pectin contains some sugar. If you're looking to make jam with less sugar, your best bet is an official recipe from a trusted source, such as the USDA or Ball. The bottom line is that this isn't a time to improvise.

Get the Recipe: Low Sugar / No Sugar Strawberry Jam

So what about botulism?

If you've looked into canning at home before, you've probably been warned about botulism, a severe illness caused by toxins from the Clostridium botulinum bacterium. Botulism attacks the body's nerves and can even cause death, so following directions from trusted canning authorities is of the utmost importance. Check out these tips from the FDA or contact your local extension office for more information. The most important thing is to respect the scientific laws at play, so make sure your equipment is sterilized and intact, and make a point to ensure that temperatures and pH levels are exact — the process will go a lot better if the requirements are in place.

Which canning method do I use?

Since jams are acidic, they work best with the water bath method. A nice thing about water bath canning is that it's a less intense process and doesn't require special equipment, such as a pressure canner. The materials necessary for water bath canning are much easier to find: two pots (an extra-large one for sterilization and a five or six-quart metal or glazed cast-iron pot), jar grabbers, a metal funnel, metal ladles, canning jars, complete with lids and rings, and cloth or paper towels for cleanup.

jars of homemade strawberry rhubarb jam

How to fill jam jars

The first step of water bath canning is making sure that everything is clean. It's absolutely fine to use older jars and rings, but you'll need new lids each time for a proper seal. They also need to be dry. If you'd like, you can soak the lids in hot water for 10 minutes to soften their edges and ease the sealing process.

You'll also need to prepare your jam. Follow your favorite homemade jam recipe exactly until the final step. You'll still be letting the jam cool down, just sealed in the jars instead. When the jam is ready, use a funnel to fill the jars, leaving about an inch of air from the top. During the processing stage, the jam will expand, and the last thing you want is jam that busts out the jar. Your jam may require a little more "headspace," so check the recipe.

Take a thin, metallic spatula and run it around the insides of the jars to eliminate any lingering air bubbles. Wipe the rims with a damp paper or cloth towel to remove any residue, which could compromise the seal. Place your warm lids at the top of the almost-filled jars and screw the rings firmly, but not super tightly, into place.

How to process jam

Water bath canners can use a canning kettle, which is essentially a large stockpot with a jar rack. However, if you already have a pot that's large enough (we're talking 20 quarts), you can DIY a canning kettle with a metal rack. Fill your kettle or stockpot and bring the water to a roiling boil. Place your filled jars in the rack, and gently lower the rack into the water, ensuring that there's at least an inch of water above the tops of the cans. Cover the stockpot or kettle and let boil for 10 minutes — or whatever is required in the recipe. Then turn off the heat and let the cans cool for five minutes.

Afterwards, remove the cans with the rack or canning tongs and let them sit undisturbed for at least an hour. To prevent cracking, place the jars on a towel rather than directly on your counter. After the jars have cooled, you can check to make sure they've properly sealed by pressing on the center of the lids. The lid should be sunken in the center and not flex when pressed. If you're nearby, you may hear a "ping" which indicates a proper seal. You can also gently unscrew the ring and try to lift the lid with your fingertips. If the lid doesn't budge, you've got a good seal. Any cans that didn't properly seal should be refrigerated, and their contents eaten within two weeks.

How to store jam

Before you put your jars away, label them with their type and the date you filled them. Your future self will thank you. Your canned goods should stay in a cool, dry place, away from sunlight. A pantry or shelf in the closet or basement will work just fine. Your jams will have a shelf life of about a year, and when you do decide to open the cans, do a quick inspection for any signs of mold or odor. Additionally, take a look at the seal. If there's any sign that the seal has been compromised or broken, discard the contents.

If you had a successful yield (or just a good time), look into other canning and preserving recipes — or, stick to jam. And if water bath canning doesn't work for you, you can always try freezer jam, or picking up a jar from your favorite farmer.


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