Wash ripe or overripe plums thoroughly. In a pot, combine the plums with enough water to cover them. Bring to a boil over medium-high heat, then cover and reduce to a simmer. Cook for 10-15 minutes until soft.

Remove from heat and stir in sugar until dissolved. Allow to cool for about 20 minutes.

Mash the cooled plum mixture into a smooth puree. Strain through a fine sieve to extract juice, leaving seeds and peels behind.

Mix in a pinch of salt to enhance sweetness, adding optional black salt and black pepper if desired. Stir well.

Pour the concentrate into clean, airtight bottles and store in the fridge for 2-3 weeks.

To serve, fill a glass with the plum concentrate halfway, add ice cubes, garnish with mint leaves and lemon juice, then top with sparkling water. Stir gently.