Preserving Aroma Compounds

The aim in handling herbs and spices is to retain their characteristic aroma compounds. The volatility of these compounds means that they readily evaporate, and their reactive nature means that they are likely to be altered if they’re exposed to oxygen and moisture in the air, or to reaction-causing heat or light. To preserve herbs and spices, their tissues must be killed and dried out, so that they don’t rot, but as gently as possible, so that water is removed without removing all the flavor. Then the dried material must be kept in closed containers, in a dark, cool place. As a general rule, herbs and spices keep best in opaque glass containers in the freezer (the container should be warmed to room temperature before opening to prevent moisture in the air from condensing onto cold flavorings). In practice, most cooks keep their flavorings at room temperature. As long as they aren’t regularly exposed to strong light, whole spices keep well for a year, and ground spices for a few months. The fine particles of ground spices have a large surface area and lose their aroma molecules to the air more rapidly, while whole spices retain the aromas within intact cells.