Prep the jars and lids. Wash canning jars, lids, and bands with hot soapy water.
Sterilize jars by simmering them in water or running through a hot dishwasher cycle. Keep jars warm until filling. Place new lids in hot (not boiling) water just before use.
Peel and chop the peaches. Score an X on the bottoms, blanch in boiling water for 30–45 seconds, then transfer to ice water.
Slip off skins, remove pits, and finely chop. You want small pieces for a smooth, spreadable jam.
Prep the peppers. Finely dice the red bell pepper and mince the jalapeños. For a bolder kick, keep some seeds and membranes.
For mild heat, remove them completely.
Mix fruit, peppers, acids, and pectin. In a large, heavy pot, combine peaches, bell pepper, jalapeños, lemon juice, and apple cider vinegar. Stir in the pectin until fully dissolved. The acids help the jam set and brighten flavor.
Bring to a boil. Over medium-high heat, stir frequently until the mixture reaches a full rolling boil (bubbling hard even while stirring).
This usually takes 5–8 minutes.
Add sugar. Pour in all the sugar at once. Stir constantly to dissolve. Return to a vigorous boil and cook 1–2 minutes, stirring.
Skim foam if needed. Add salt and optional spices now; if using vanilla, add it after you take the pot off the heat.
Check the set. Turn off the heat. Place a small spoonful on a chilled plate and wait 30 seconds.
If it wrinkles when nudged, it’s ready. If not, return to a boil for another 30–60 seconds and test again.
Fill jars. Ladle hot jam into warm jars, leaving 1/4-inch headspace. Wipe rims clean.
Apply lids and screw bands fingertip-tight.
Process in a water bath (for shelf-stable jars). Submerge jars in boiling water with at least 1 inch of water above them. Process for 10 minutes (adjust for altitude if necessary). Start timing once the water returns to a full boil.
Cool and check seals. Remove jars and let them sit undisturbed for 12–24 hours.
You should hear gentle pops as they seal. Press the centers of the lids—no flex means a good seal. Label and date.
For refrigerator jam. If skipping canning, let the jam cool and store in clean jars in the fridge.
Use within a few weeks.