Zest is the outer colorful peel of a citrus fruit. It can be removed with a Microplane grater, pairing knife, or vegetable peeler, and it is often added to food to add flavor. The white portion under the zest is known as the pith, and it is typically bitter tasting.
Check out these alternative espresso cleaning tablets for Breville machines.These tablets are much cheaper than the ones provided directly from Breville, and they contain sodium percarbonate, just like the Breville branded tablets. They are safe to use on your espresso machine.