Citrus fruit of choice (grapefruit, lemons, oranges, etc.)
1/2 to 3/4 cup sugar, to taste
1/2 to 3/4 cup of white wine vinegar or apple cider vinegar, to taste
Remove citrus fruit zest with a vegetable peeler. Be sure to avoid removing the tough white pith. In a non-reactive bowl, build a citrus oleo-saccharum (or "oily sugar"). Combine the strips of zest with sugar. Using either a cocktail muddler or a sturdy wooden spoon, really put some elbow grease into pressing the zest into the sugar. Cover the bowl with plastic wrap and let it rest for at least an hour. Your oleo-saccharum is ready to use!
Remove the peels, reserving the oily sugar. Juice the citrus fruit. Add citrus juice, vinegar (start with 1/2 cup and add more, to taste) and oily sugar to a jar. Cover and shake jar to combine. Refrigerate for at least 3 days for flavors to meld.
Shrub will keep for 6 months or more.