Berry Jam

5 cups raspberries, blackberries, blueberries, or sliced strawberries, or any combination
2 cups sugar
1 tablespoon lemon or lime juice
1/4 teaspoon salt

Place all the ingredients in a large pot, set it over medium-high heat, and stir constantly until simmering.

Reduce the heat to low and simmer until thickened, 15 to 18 minutes, stirring often, especially during the last few minutes as the berries break down.
Spoon into glass canning jars or other nonreactive heatproof containers. Seal and store in the refrigerator for up to 1 month.