Hyssop leaves can be preserved by drying. They should be picked on a dry day at the peak of their maturity and the amount of active ingredients is highest. They should be dried quickly, away from bright sunlight in order to keep their aromatic ingredients and prevent oxidation of other chemicals. Good air circulation is required, such as an airing cupboard with the door left open, or a sunny room, aiming for a temperature of 20-32°C. Hyssop leaves should dry out in about six days, any longer and they will begin to discolor and lose their flavor. The dried leaves are stored in clean, dry, airtight containers, and will keep for 12–18 months.