Gently wash the berries and drain well.
Remove the caps and cut the berries into quarters.
Put into a large nonreactive pot, and pour the sugar and salt over them.
Set the pot over medium heat and watch carefully, gently shaking the pot as needed rather than stirring, until the berries come to a simmer.
Cook at a lively simmer, skimming carefully any scum that is released, for 12-15 minutes, just until the fruit is tender and the syrup clear.
Spoon the hot preserves into sterilized jars, or cool and store in the refrigerator.