Derived from seaweed, agar is a vegetarian alternative to gelatin. If you cannot locate agar, you can use unflavored gelatin. You will need 4 envelopes. Soften gelatin in 1 cup of the juice. Boil the remaining 3 cups and stir into the softened gelatin mixture. Gelatin will need to be refrigerated for each of the subsequent steps, as it does not set up at room temperature (as agar does).