Blackberries are only in season for a month or two in late summer, so if you want a supply of sweet, flavorful blackberries to eat all year round, you need to break out the freezer bags and jelly jars. Steps for freezing blackberries depend on what you ultimately plan to do with them, so it's best to know where your berries are headed before you pop them in the freezer. Frozen blackberries keep for up to 12 months.
Choose a Use
You may want to freeze your berries plain, sugared or syruped, depending on what you want to do with them later. If you plan to bake them into quick breads or muffins, there's no need to add any sugar when you freeze them. If the berries are to be the strongest flavor in the eventual recipe, such as in a pie or tart, freeze them with sugar to retain their sweetness. Pack berries in syrup to serve unaccompanied or as part of a fruit salad.
Prepare the Berries
Pick out any squashed, unripe or overripe berries and discard them. Wash the rest gently, being careful not to damage them. Drain them thoroughly, then spread them on a paper towel or dish towel. Allow berries you intend to freeze without sugar to dry thoroughly -- making sure they are dry to the touch before you freeze them helps ensure that they don't stick together in the freezer. This is also the time to puree any berries you want to freeze in blended form.
Pureed or Syruped: Pack Jars
For berries you are freezing pureed or in syrup, disinfect freezer-safe glass or plastic jelly jars in hot, soapy water, then allow them to cool. Mix each quart of pureed blackberries with 1/2 to 3/4 cup of sugar and pour the mixture into jars. If you're using pint jars, leave 1/2 inch of space at the top; leave 1 inch for quart jars. To pack berries whole in syrup, dissolve 2 1/2 parts sugar in 4 parts water. Fill pint jars loosely with blackberries to 1/2 inch from the top; fill quart jars to 1 inch from the top. Pour the syrup in to cover the blackberries, and seal the jars tightly. Place the jars in the freezer.
Sugared or Plain: Freeze Bags
Toss blackberries for pies or tarts in sugar. Lay them out on a tray and freeze them until they begin to harden, then remove them, place them into freezer-safe zip-closure bags, squeeze out the excess air or suck it out with a straw, and return the bags to the freezer. For berries you intend to freeze plain, do the same, but omit the sugar coating. Plain berries don't keep as long in the freezer as sugared or syruped ones; use them within eight months rather than 12.