Despite its reputation, the cottony white layer of pith on citrus fruits (grapefruit excepted) isn’t bitter. In fact, it’s completely flavorless. (It’s true—slice off a piece and try it for yourself.) And the zest tastes only subtly bitter.
So why does your homemade lemonade sometimes turn out bitter?
It happens when the pith and zest are abraded together, as they often are when preparing citrus-based drinks: Acid and enzymes convert the peel’s flavorless compounds into new ones with pronounced bitterness.
If you aren’t going to be rubbing the two substances together, don’t worry about leaving some pith on your zest. But if you are, as in our Lemonade Concentrate recipe, we recommend using a vegetable peeler to harvest the zest with minimal pith. This zest will impart just enough bitter flavor to add complexity, but not enough to obscure the drink’s sweet-sour balance.