Grapefruit and tangerine zest contain more pith relative to the flavorful oils compared to lemon zest. Therefore, you need to be more careful to avoid grating too deeply and including the bitter white pith.
The zest of citrus fruits contains aromatic oils that contribute significantly to their flavor. These oils are concentrated in the outermost layer of the peel, the flavedo. Beneath the flavedo lies the pith, the white, spongy layer that is quite bitter.
Lemons generally have a thinner pith layer compared to grapefruits and tangerines. This means that when zesting a lemon, it's slightly easier to obtain the flavorful zest without accidentally grating into the bitter pith. Grapefruits and tangerines, with their thicker pith, require a more delicate touch. If you zest too aggressively, you'll incorporate a larger proportion of pith, resulting in a noticeably bitter and less pleasant flavor in your dish. The key is to use a light touch and only remove the colored part of the peel.
The difference in taste is directly related to the amount of pith included in the zest. More pith equals a more bitter flavor, which can overpower the desired citrus notes.
Use a microplane zester for all citrus fruits. Its fine blades allow you to remove only the outermost layer of zest, minimizing the risk of including the bitter pith, especially when working with grapefruits and tangerines.