Wash the apples and peppers thoroughly. Peel and core the apples, remove the jalapeño seeds and membranes if you prefer less heat, and chop every ingredient very finely without processing it into a completely smooth purée.

Place the chopped apples, red bell pepper, jalapeños, apple cider vinegar, optional cayenne, and optional salt in a large stainless-steel saucepan. Stir well so the vinegar coats the fruit and vegetables.

Bring the mixture to a full boil over medium-high heat, stirring frequently. The apples and peppers should soften slightly while still providing tiny pieces throughout the finished jelly.

Add all 5 cups of sugar at once and stir until fully dissolved. Return the mixture to a vigorous boil that cannot be stirred down, watching closely because the sugary liquid will foam as it heats.

Stir in the liquid fruit pectin only after the fruit, vinegar, and sugar mixture has reached a full boil. Boil hard for 1 minute while stirring constantly, then remove the saucepan from the heat.

Skim off any foam from the surface for a clearer jelly. Ladle the hot jelly into hot, sterilized half-pint jars, leaving 1/4 inch headspace, then wipe the rims clean and apply two-piece lids.

Process the filled jars in a boiling-water canner for 10 minutes, increasing the processing time according to local altitude guidelines. Remove the jars carefully and let them cool undisturbed for 12–24 hours before checking the seals.