Expression

Expressing a peel means twisting or gently squeezing a piece of citrus skin, cut with a bit of the colored zest and a little pith, over the top of a finished drink so the tiny oil glands in the peel burst and mist across the surface. It is a garnish technique, not a flavoring ingredient added into the liquid itself.

The oils in citrus peel are intensely aromatic, and since smell drives most of what we perceive as flavor, a well expressed peel changes the first impression of a drink dramatically even though almost none of the oil actually lands in the glass. An Old Fashioned or Martini finished this way smells noticeably different than one where the peel was simply dropped in without expressing it.

A sharp peeler or zester that takes a clean strip without much bitter white pith underneath gives the best results, since pith adds bitterness rather than aroma. After expressing the oils over the drink, many bartenders then run the peel around the rim of the glass before dropping it in. A common mistake is using a dull tool that tears the peel and releases barely any oil at all.