The dark purple, nearly black fruit of the blackberries is both sweet and tart. Used in jams and jellies, pies and in syrups, blackberries are full of many small seeds similar to strawberries. Unlike strawberries, though, blackberry seeds are hard. The seeds are edible, but if you don't like the texture or are making fruit leather the seeds are undesirable. As the seeds are very fine, complete removal is is difficult but most of the seeds can be easily removed with the help of common kitchen tools.
Place the blackberries in a colander in the sink. Wash thoroughly under running water, removing any remaining stems or leaves.
Set a fine mesh metal sieve over a bowl. Place a handful of blackberries into the sieve.
Push the berries through the sieve with your hands. Use a metal soup ladle or the bottom of a glass to push the berries if you have trouble doing it with your hand.
Discard the seeds in the sieve once the handful of berries has been pushed through. Continue pushing the berries through the sieve one handful at a time until all the berries have been strained, discarding the seeds after each batch.
Check the strained berries for seeds. Strain a second time if lots of seeds are still visible, but keep in mind some seeds are unavoidable.