Fresh Raspberry Preserves

In a medium saucepan, cook the raspberries with the salt over moderate heat until they start to break down and release their juices, about 5 minutes. Add the vinegar and sugar and cook over moderately low heat, stirring occasionally and crushing the berries with the back of a spoon, until very thick, about 45 minutes. Transfer the preserves to a small bowl and let cool to room temperature, then refrigerate.