The zest of a lime is the outer green layer of peel, which contains fragrant and flavorful oils.Lime zest adds intense flavor to cocktails, desserts and a number of other recipes.ollect the zest and place it in a small bowl. Once the whole lime has been zested, or you have as much zest as you need, set aside the lime for later use. Use a knife to scrape the zest off the cutting board and into a small bowl, or directly into the dish you are cooking as instructed by the recipe.