Q:

What is "Zest" - In particular: lime/lemon zest?

I saw a recipe that asked for Lime Zest and was wondering what it was?

A:

The very thin outside layer of the Lime, Lemon, Orange, and other citrus. It contains aromatic and flavorful oils that will enhance your meals.
When you zest your citrus fruit (usually with a fine grater) you need make sure that you only pull off the zest and not the white pith that lies underneath. The pith is bitter and generally not something you want in your dish.

A:

It's the colorful outer layer of the peel. The white part is the pith, and you don't want that as it imparts bitterness.
You can remove the zest by using the part of a cheese grater that you would use for parmesian cheese.  If you're really careful, you can also use a vegetable peeler, but it's difficult to avoid the pith.

