Cut lemons and limes in half and juice them using a citrus juicer or hand juicer, pressing firmly to extract all the juice.

Measure 1 cup of the fresh lemon juice into your mixing bowl or pitcher.

Measure 1 cup of the fresh lime juice and add it to the bowl or pitcher.

To make simple syrup, combine 1/4 cup sugar and 1/4 cup water in a small saucepan; heat over medium heat, stirring until the sugar dissolves, about 2 minutes, then allow to cool completely.

Add 1/2 cup of the cooled simple syrup to the citrus juices in the mixing bowl.

Whisk or stir the mixture thoroughly for about 30 seconds to fully incorporate the syrup with the juices.

Strain the sour mix through a fine mesh strainer into a glass storage bottle to remove pulp and seeds.

Seal the bottle with a tight-fitting lid and refrigerate. The sour mix is ready to use and will keep for up to two weeks.