One medium-sized lemon yields about 1 tablespoon of zest, as well as a couple of tablespoons of lemon juice. The zest from other citrus fruits, such as limes or grapefruits, can also be substituted for lemon zest.
To zest a lemon, peel away just the yellow part of the lemon, leaving the white pith behind. Use a microplane to grate the zest away from the lemon, or use a standard peeler to pull it away in chunks and chop it finely before use.
The Asian herb lemongrass may also be substituted for lemon zest, as it has a similar lemon flavor. Lemon leaves impart a similar flavor, but they provide a very different texture.