Preparation – Select firm, ripe fruit soft enough to yield to slight pressure. Sort and wash. Leave whole or cut in halves or quarters and pit.
Syrup Pack – Use cold 40 to 50 percent syrup, depending on tartness of fruit. For a better quality product, add 1/2 teaspoon (1500 mg) ascorbic acid per quart of syrup. Put plums directly into cold syrup in container, starting with 1/2 cup syrup to a pint container. Press fruit down and add syrup to cover, leaving headspace. Place a small piece of crumpled water-resistant paper on top to hold fruit down. Seal and freeze.
Plum Sauce – Boil well-ripened clingstone plums without water until soft; then remove pits and skins. Continue cooking the pulp and juice until it thickens. Add 1 part sugar (with spices, if desired) to 4 parts plums.
Cool and package, leaving headspace. Seal and freeze.
In addition to a dry pack, unsweetened fruit can be packed in water, unsweetened juice or pectin syrup. Unsweetened packs generally yield a product that does not have the plump texture and good color of those packed with sugar. The fruits freeze harder and take longer to thaw. The pectin syrup is often used for fruits such as peaches that retain their texture better than if frozen in water or juice.