Chlorophyll is extracted from plants — typically fescue and alfalfa — and then chemically modified (or stabilized), displacing the magnesium from the core of the molecule and substituting it with copper. The resulting stable, water soluble colouring is called sodium copper chlorophyllin. Copper chlorophyllin is permitted as a food colouring in the European Union; however, in the USA, its food use is limited to dry citrus beverages.
Copper chlorophyllin is very heat, light and pH stable compared to magnesium based chlorophyll found in nature. It is available as a water soluble liquid or powder; an oil soluble version is also available.