Pyrethrum Flowers are Processed to produce Pyrethrins
Refined pyrethrum extract has been commercially produced for more than 60 years. As a natural product, it is not unexpected that pyrethrum presents challenges in both processing and analysis. The key to extraction and refining is maintaining high recoveries of pyrethrins throughout processing. To maintain the high recoveries, proper handling of the flowers and extracts must be tracked to insure there are not losses due to fermentation, excessive exposure to heat, or inadequate extractions.
Pyrethrum flowers are harvested by hand in East African countries- Kenya, Tanzania, and Rwanda - and are dried in the open air to avoid fermentation that can lead to pyrethrin losses. The dried flowers are placed into burlap sacks for transportation to processing facilities where they are ground into powder for extracting. Good quality dried flowers contain approximately 1.4% to 1.8% pyrethrins.
The primary extraction from ground pyrethrum flowers results in a crude pyrethrum extract that can vary from semi-solid to a viscous liquid and is similar to a black tarry substance. In Tasmania, Australia mechanical cultivators are used to cut the pyrethrum flowers and stack the cut flowers and stems in wind rows for drying under the sun prior to collection. The dried material is collected and pelletized for extraction to produce a crude extract similar to other producers containing approximately 30% pyrethrins.
Crude extract is not suitable for use in formulations as it still contains excessive levels of vegetable waxes and resins and high levels of color bodies that will result in staining. Therefore further extraction is conducted to remove excess vegetable waxes, resins and color bodies.
Each of the three primary refiners of pyrethrum in the world - Kenya, MGK or BRA - have some unique aspects of their processing, but they all result in a clear, amber liquid that contains anywhere from 20% to 55% pyrethrins. The standardized pyrethrins solution is typically blended with synergists, emulsifiers and solvents into the various formulations to kill insects.