Canning Jam, From Preparing the Jars to Testing the Seal

REFRIGERATOR jams will last for weeks, maybe even a few months, when kept cold and tightly sealed. You can also freeze the jams for up to six months before they start to lose their texture. But any of these recipes can also be canned for longer storage — up to a year. And canning means you can keep the jams in the pantry, freeing valuable fridge space.

Unless you’re making vats of jam, I recommend buying small jars, either 4- or 8-ounce, because they will fit easily in the average stockpot and are easier to maneuver. (By the way, you can reuse canning jars, but make sure to buy new lids to ensure a good seal.)

Once you have your jars, here’s what to do.

1. Fit a large pot with a rack, or line with a folded kitchen towel. Fill 2/3 with water and bring to a boil. Add canning jars and boil for 10 minutes. Jars may be left in the warm water in the pot until ready to be filled. (Alternatively, you can sterilize jars by running them through a dishwasher cycle, leaving them there until ready to fill.)

2. Place canning rings in a small saucepan, cover with water and bring to a boil. Turn off heat and add lids to soften their rubber gaskets. Rings and lids may be left in the water until jars are filled.

3. Remove warm jars from the pot and bring water back to a boil. Ladle hot jam into jars just up to the base of the neck, leaving 1/2 inch at the top. Wipe jar rims clean with a damp towel. Place lids on jars, screw on rings and lower jars back into the pot of boiling water. The water should cover the jars; if not, add more. Boil jars for 10 minutes. Transfer jars to a folded towel and allow to cool for 12 hours; you should hear them making a pinging sound as they seal.

4. Test the seals by removing rings and lifting jars by the flat lid. If the lid releases, the seal has not formed. Unsealed jars should be refrigerated and used within a month, or reprocessed. (Rings and jars may be reused, but a new flat lid must be used each time a jar is processed.) To reprocess, reheat filling to the boiling point (as in Step 3), then continue as before.