Oleo-saccharum sounds like an ancient nostrum to cure an obscure disease, but it’s actually a mixture of sugar and citrus that brightens a punch. Its use has been revived by historian David Wondrich, who discovered that early punch makers would rub whole citrus fruits on a stiff cone of sugar, infusing the sugar with some of the zesty tang of the oils in the peels. An easier, more convenient way to prepare an oleo-saccharum (oleo, for short) is to  peel the citrus, then  toss the peels with granulated sugar in a sealed container, such as a mason jar. Let it sit for twelve to twenty-four hours, shaking from time to time; the sugar will extract oils from the peels.  Pour the same amount of water as the original amount of sugar into the jar, shake to dissolve, and strain. You’ll be left with a syrup that adds a welcome layer of citrusy goodness and an ineffable crispness to the punch. It’s a minor hassle with major returns.
Four Classic Punch Recipes