Lemon zest is the oil-rich outer skin of a lemon. The volatile oils in the zest make it extremely flavorful, which is why some recipes call for it in addition to lemon juice or lemon essence. The process of removing lemon zest is known as “zesting,” and many kitchen supply stores sell tools which are specifically designed to remove zest. Other citrus fruits can be zested as well for an infusion of intense flavor in a wide range of dishes.
The peel of a citrus fruit contains two top layers; the zest, and the pith. The zest is shiny, brightly colored, and textured; it is the outer surface of the fruit which consumers can directly see. The pith is a white, fibrous membrane directly below the zest which helps to protect the fruit inside. While the pith of a citrus fruit is often edible, it is not very exciting, so when a fruit is zested, the zest is gently separated from the pith to isolate the flavor.
There are a number of ways to zest a lemon. Some zesters work like graters, delicately shredding the zest so that tiny flakes are removed. Others take the zest off in long strips; strips of zest make great decorations for desserts, and they can also be candied, fried, or suspended in custards by adventurous cooks. Deft cooks can remove lemon zest with a paring knife or vegetable peeler, although this requires a light hand to take the zest without the pith.
In baked goods, this ingredient can be used to add a lemony flavor to the finished food product. The natural oils in the zest will slowly leach out through the cooking process, infusing the food with flavor. Individual pieces of zest will also crack open in the teeth of consumers, producing a sudden burst of lemon flavor. Lemon zest can also be used as a food seasoning, or it can be added to various mixed drinks and beverages.
Most recipes call for fresh lemon zest, although a candied version is acceptable in some recipes. Candied zest typically includes the pith as well; the candying process softens the pith and makes it more flavorful, so this inclusion is usually not objectionable. This ingredient is also sometimes mixed with spices like lemon pepper, in which case it may be dried after the oils have been released through crushing. If you have a particularly good batch of lemons, you can zest them and freeze the zest for future use.