Spices and herbs at a grocery shop in Goa, India. A spice is a seed, fruit, root, bark, berry, bud or vegetable substance primarily used for flavoring, coloring or preserving food. Spices are distinguished from herbs, which are parts of leafy green plants used for flavoring or as a garnish.Many spices have antimicrobial properties.This may explain why spices are more commonly used in warmer climates, which have more infectious disease, and why the use of spices is prominent in meat, which is particularly susceptible to spoiling.mall seeds, such as fennel and mustard seeds, are often used both whole and in powder form. The flavor of a spice is derived in part from compounds (volatile oils) that oxidize or evaporate when exposed to air. Grinding a spice greatly increases its surface area and so increases the rates of oxidation and evaporation.