Step 1: Sterilize your canning jars and lids. Wash them thoroughly in hot, soapy water, then rinse. For jars, either boil them in a large pot for 10 minutes or run them through a hot sanitize cycle in your dishwasher. Keep them hot until ready to fill. Lids and bands should be simmered (not boiled) in hot water according to manufacturer instructions.
Step 2: Prepare your peaches. Bring a large pot of water to a rolling boil. Score a small 'X' on the bottom of each peach. Carefully drop a few peaches into the boiling water for 30-60 seconds, then immediately transfer them to an ice bath using a slotted spoon. This process, called blanching, helps the skins slip off easily. Peel, pit, and chop the peaches into small pieces or mash them to your desired consistency for this peach jam recipe.
Step 3: In a large, heavy-bottomed pot or Dutch oven, combine the prepared peaches and fresh lemon juice. Stir well to combine.
Step 4: Add the granulated sugar to the peach and lemon juice mixture in the pot. Stir thoroughly until the sugar begins to dissolve. Bring the mixture to a full rolling boil over high heat, stirring constantly to prevent sticking. A full rolling boil is one that cannot be stirred down.
Step 5: Continue boiling, stirring frequently, until the jam reaches its setting point. This can take anywhere from 15-30 minutes, depending on your fruit and heat. To test for a set, you can use the cold plate test (drop a spoonful on a chilled plate, if it wrinkles when pushed, it's ready) or a candy thermometer (jam sets around 220°F/104°C).
Step 6: Once the jam has reached its setting point, remove it from the heat. Carefully skim off any foam that has risen to the surface using a metal spoon. This makes for a clearer, more appealing jam.
Step 7: Ladle the hot peach jam into the hot, sterilized jars, leaving about 1/4 inch of headspace. Wipe the rims clean with a damp cloth to ensure a good seal. Place the hot lids on the jars, then screw on the bands until finger-tight.
Step 8: Process the filled jars in a boiling water canner for 10 minutes (adjusting for altitude as necessary). After processing, carefully remove the jars from the canner and place them on a towel-lined counter, leaving space between them. Do not disturb for 12-24 hours. You should hear popping sounds as the lids seal.
Step 9: Check seals. If any jar did not seal (the lid will not be concave), refrigerate that jam and consume it within 3 weeks. Properly sealed jars of this peach jam recipe can be stored in a cool, dark place for up to 1 year.