Look for plump firm plums with no signs of wrinkled or split skin. When ripe their skin will be a deep red-black colour. Once ripe plums should yield slightly to gentle pressure. Until at this stage store in a single layer at room temperature. Once ripe store in a plastic bag in the fridge for 2 to 3 days. Simply wash plums gently in cold water. If using for cooking or to make jams and sauces halve and remove the stones first.