Place ripe, but not overripe, berries in a bowl, mash them with a spoon, and pile them into a linen bag. Tie the bag securely above the berries and hang it up so that the juice flows out gradually. Let the juice settle and carefully decant the clear juice into a preserving pan, filling it halfway. For 1 lb juice, use 1½ lbs finely pounded sugar (i.e., for 1 glass juice, use 1½ glasses sugar). Mix to completely dissolve the sugar. Cover the saucepan with a lid and set it over a rather high fire. When it begins to boil, which can be recognized by the jingling handles of the pan, raise the lid and watch that the juice boils thoroughly but does not boil over. Then remove from the fire and thoroughly wipe off the lid. When the syrup stops steaming, replace the pan on top of the stove, covered, and let it come to a boil. Repeat this three times and then finish cooking over a low fire, testing with a spoon so that it does not overcook and with a spill so that it does not reduce to the mark itself. Toward the end, the lid may be removed.