Add agar agar powder or flakes. Stir and continue to simmer for 2 minutes. If using flakes, you may need to simmer for a bit longer to ensure the flakes have completely dissolved.
Pour into a shallow bowl or dish and refrigerate 30 minutes.
Notes
Use any juice you'd like, although agar agar doesn't set well with high acids, like lemon juice.To make the purple "gelatin," steep 2 tablespoons of dried butterfly pea flowers in 4 cups of apple juice until the desired color is achieved. Strain juice and discard flowers before bringing to a simmer and adding agar agar.