Avid blackberry users agree that blackberries do not freeze well if you are looking for a whole product to put on cereals, garnish recipes or just having a bowl of plump blackberries. The best way is to “can” them.
For those that want to freeze them, the way to do it is to spread them out on wax paper on a cookie sheet then placing it in the freezer. Place the frozen blackberries in a bag and quickly put back in the freezer. Pour out what you want to use and again quickly replace in the freezer. If you are not worried about the convenience of pouring out what you want freeze whole blackberries in syrup. The product will be excellent but the berries may be a little softer than the hot raw pack suggested below.
Most recipes call for a crush product. If you know which recipes you will be using determine what aliquot sizes you will need. Purchase an appropriate size container(s) and process your berries ahead of time. Usually mash the berries or briefly grind them in an electric food blender, strain them through a wire mesh screen and place in a container and freeze them immediately. Please bear in mind that much of the nutriceutical value is in the seeds and pulp residue [see below]. Therefore the less you leave on the wire mesh screen, the better it is for you.
The best looking berries will be obtained with the raw pack method. Use quality wide mouth canning jars, sterilize and fill snugly without crushing with raw blackberries. Pour hot syrup over the berries leaving ¼ to ½ inch of space under the lid. See the recipe for canning syrup below. The lid should be not tight to allow for expansion of air in the head space but tight enough to keep water out. Place in a hot water bath with water covering the top of the jar with 1 inch of water and bring to a simmer. Start timing once the water begins to boil/simmer. Use 15 minutes for pints and 20 minutes for quarts. Remove from the hot water bath and tighten lid immediately.
Use ½ cup of blackberries per quart of canning syrup. Crush or blend the berries in an electric blender and strain. Add to 4 cups of water and bring to a simmer. Add sugar depending on whether you want very light [½ cup sugar/ qt ], light [1 cup sugar/qt], medium [1 ¾ cup of sugar/qt], heavy [2 ¾ cups sugar/qt] or very heavy [4 cups sugar/qt] syrup. Pour hot over raw pack as instructed above. It may also be used on whole fresh frozen blackberries. Cool before adding to the berries to be frozen.
Blackberries and blueberries and other fruit are healthy for you: They are considered a nutriceutical. They are very high in Elegiac acid, resveratrol, beta carotene, folic acid and Resorcinol which are strong free radical scrubbers. Where possible leave the seeds in the recipe or when told to discard, save them and make a puree to be included in breads and muffins. The seeds are very high in these compounds. Blackberries are also very high in vitamins A and C, potassium, fiber and other bioflavonoids all of which are suppose to reduce the risk of cancer, reduce cholesterol levels, protect against heart disease and slow the ageing process. Also they contain anthocyanosides which may act as antibacterial agents and are thought to promote urinary health. There is even some claims that they promote better vision. All this needs more confirmation with solid science research. But, all the research to date seems to back what folk medicine has been saying for years, "Fruits are good for you!" Generally the rule of thumb seems to be that the blacker the fruit as you progress from strawberries to blackberries the greater the content of these compounds.