Walk into a room after someone has peeled an orange, and the fragrance is positively uplifting. This instant aroma comes from essential oils in the zest, the colored outer layer of citrus skin. Zest is the colored portion of the rind of the orange. It is not the underlying white, pith portion of the peel. The outer-most layer of the rind can be grated or thinly veneered with a tool called a zester, to produce orange zest. The grating action creates a pile of orange zest, which is usually left to dry overnight before being stored in airtight herb bottles. Zest is popular in cooking because it contains the oil glands and has a strong flavour similar to the fleshy inner part of the orange. Always grate the colored part of the rind and not the white pith underneath because it can be bitter.