Plants are picked at their peak, washed, flash-frozen, and dried at very low temperature in a vacuum chamber. Freeze-dried herbs are encapsulated for sale, or stored for later use to make extracts. Herbal teas only provide the water-soluble compounds, and the body cannot effectively extract some active compounds from dried, encapsulated herbs. Alcohol and glycerin also preserve an herb's chemical constituents for two years or more. Extracts can be made from fresh or dried herbs .
Some herbs lose significant medicinal potency when dried, while others gain potency after drying.
There are relatively few herbs whose medicinally active compounds have been clearly identified. And in many cases, an herb's beneficial effects depend on all its compounds acting together. The actual amount may be greater. It is important to note that the presence of a specific amount of a certain compound cannot by itself guarantee efficacy. At this point, consumers and retailer alike must rely largely on manufacturer's claims and reputation for integrity, as testing each extract would be prohibitively expensive.