Put all in a pot in a stainless steel pot on medium heat and boil for 15 minutes until soft.
Let the syrup cool, then blend. The plum concentrate syrup is ready. Transfer to a jar and store in fridge for 3-4 weeks. You can freeze it too for later use.
For Plum Lemon Soda
Mix water, ice and syrup. Pour in glass and top with lemon soda. Garnish with mint leaves and serve chilled.
For Plum Lemonade (Slushy)
Put plum syrup and ice in a blender and pulse until ice is slushy for about a minute.