Toss chopped peaches in lemon juice to prevent browning.
Place the peaches and lemon juice in a deep, heavy-bottomed saucepan.
Add the pectin (but not the sugar) and bring the mixture to a boil. Cook 2-3 minutes, mashing the peaches for a smoother preserve or leaving them whole for a chunky peach jam.
Add the sugar and stir to incorporate. Return the pot to a boil and cook for 1 minute, stirring to distribute heat.
Turn off the heat and ladle the finished peach jam into jars, leaving 1/4 inch headspace. Cap with 2 part lids.
Store in the refrigerator for immediate use, or freeze for up to 6 months, or water bath can for longer storage.
Canning Peach Jam (Optional): If canning, process jars in a water bath canner for 10 minutes if below 1000 feet in elevation (adjust for altitude by adding 1 minute for every 1000 feet in elevation rise). Remove jars to cool on a towel on the counter and check seals after 24 hours. Store any unsealed jars in the refrigerator for immediate use.
Properly canned peach jam should maintain quality on the pantry shelf for 12-18 months.
Notes
Low Sugar Peach Jam ~ Standard pectin requires at least 50% sugar to gel properly. You can reduce the sugar to 4 cups and the jam will still have a loose set. If you'd like to reduce the sugar further, use a low sugar pectin such as Pomona's pectin and follow the instructions on the packet. Peach Jam with Liquid Pectin ~ If using liquid pectin, you'll need at least 7 cups of sugar to get the jam to gel properly. I'm not a fan of liquid pectin, and I don't suggest using it, as that's just too darn sweet.A note on lemon juice ~ The lemon in this recipe is optional and helps to add a bit of tartness to balance the sugar. Omit it if you'd like, but I'd strongly suggest it for improved flavor. Feel free to use fresh lemon juice or bottled, since it's not added for canning safety. White Peaches ~ White peaches are less acidic than yellow peaches, and they're not approved for canning. If you make peach jam with white peaches, preseve it as a refrigerator or freezer recipe (but don't can it).