Step 1Brush or lightly rinse the berries without submerging them in water. Remove the hulls, leaving the berries whole. Combine the berries, sugar and juice in a non-aluminum bowl. Allow the berries to macerate at room temperature, stirring occasionally, for at least 3 to 4 hours. The mixture can be covered and refrigerated overnight at this point.
Step 2Divide the berries and the juice (it will yield approximately two pints) in equal proportions into 2 or 3 wide, shallow pans -- a large copper-bottomed risotto pan or cast-iron enameled pot is good. If using a thin pan, use a heat diffuser to avoid hot spots. Bring the mixture to a boil over high heat, skim the foam that collects on the surface, then reduce the heat to low. Make sure bubbles continue to break the surface. Stir the mixture gently, pushing the berries in a gentle circle, taking care not to slice through them or break them up. Part of the charm of the jam is the proportion of whole berries.
Step 3After about 20 minutes, the berries will give up additional juices and appear to be floating. Press them with a wooden spoon and skim off foam, placing the foam in a bowl near the stove. As the foam juice collects, skim it, and return the red juice to the pan.
Step 4Continue cooking the berries, stirring and skimming occasionally for 3 to 4 hours. The cooking time will vary depending on the berries, the amount of sugar, the type of pan and the heat from burners. The jam is almost done when it turns dark red, the ratio of berries to juice is about equal and it begins to coat a wooden spoon. At the end of 3 hours, tart berries cooked with more sugar should be done. It may take closer to 4 hours for berries cooked with the lesser amount of sugar. If necessary, after 4 hours, raise the temperature to quickly cook off excess water, stirring to prevent scorching. To test for how the preserves will set, put a spoonful on a frozen plate and see how it gels. Turn off heat and can in the usual way, or allow to cool and refrigerate and use within several days.