The raspberries you choose for freezing need to be perfectly ripe, as once they’re frozen they cannot ripen any further. Choose raspberries that are of a good size, firm but ripe and plump. Avoid using any raspberries that are mushy, falling apart or moldy. Remove any undesirable ones, as well as pieces of leaves, twigs, etc., before preparing the raspberries for freezing. Make sure the raspberries are dry before freezing.