verjuice _ The sour juice of green or unripe grapes, crab apples, or other fruit, especially when made into an acidic liquor. This liquor was once much used in cooking, as a condiment, and for medicinal purposes.
– A Sea of Words : A Lexicon and Companion for Patrick O’Brian’s Seafaring Tales by Dean King with John B. Hattendorf and J. Worth Estes.