Macerate the plant material to make pulp. Optional methods of macerating include finely mincing with a knife, grating and processing in a blender or food processor.
Pour the pulp into a glass container. Add an equal amount of tepid water to the container. Stir the pulp and water for several minutes with a metal stir stick.
Line a different glass container with a paper filter. Place the pulp and water mixture in the filter. Filter the juice into the second container. Squeeze the filter firmly.
Scrape the pulp from the filter, and mix it with more warm water, as you did previously. Filter the resulting juice in the same manner using a new paper filter. Repeat the process of extracting the juice from the pulp at least one more time.
Put the juice in a pot on a stove. Turn the stove burner on low-medium heat, and bring the juice to a simmer. Heat the juice for several minutes until its water portion cooks off and a syrup develops.