Place the muscadines and water in a large saucepan over medium heat. Cook for about 10–15 minutes, stirring occasionally, until the grapes soften and begin releasing their juices.
Mash them gently with a potato masher.
Pour the cooked muscadines through a food mill or fine-mesh sieve, pressing firmly to extract as much pulp and juice as possible.
Return approximately 3 cups of muscadine pulp/juice to the saucepan.
Add sugar, minced jalapeño, rosemary sprig, lemon juice, lemon zest, and salt.
Bring the mixture to a boil over medium-high heat, stirring frequently.
Lower the heat slightly and continue cooking for 20–30 minutes, stirring frequently, until the mixture becomes glossy and noticeably thickened.
Remove the rosemary during the last few minutes if you want a subtle rosemary flavor. Leave it in longer for a stronger flavor.
Transfer the preserves to clean jars and let it cool. The preserves will thicken as they cool.
Refrigerate for up to 3 months.
