Oleo saccharum and citrus peels

Most of a lemon's perfume lives in the skin, not the juice. Pinch a strip of peel over a glass and you can see it: a fine mist that catches the light and lands on the surface of the drink. Oleo saccharum, Latin for oil sugar, is the slow version of that pinch. Sugar sits on the peel overnight, draws the oil out, and turns into a syrup that tastes like the lemon smelled.

What you need

• 4 unwaxed lemons, washed and dried. Waxed supermarket fruit will not give up its oil as freely; scrub it under hot water if that is all you have.
• 180 g fine white sugar, about 45 g per lemon. Caster or superfine dissolves best.
• A Y-shaped vegetable peeler, a kitchen scale, a wide jar with a lid, and a muddler or wooden spoon.
• For the punch shrub: 180 ml / 6 oz fresh lemon juice, roughly the juice of the same four lemons.
• For expressing peels at the bar: a channel knife or peeler, and a small paring knife.

Steps: oleo saccharum

1. Peel each lemon in long strips, pressing lightly so you take the yellow and leave the white pith. Pith is bitter, and it carries no oil worth having. Reserve the peeled fruit for juice.
2. Weigh the peels; four lemons give about 40 to 50 g. Put them in the jar with the 180 g of sugar and toss to coat.
3. Press the peels into the sugar with the muddler, a few firm twists, until the sugar looks damp. This is optional; it shortens the wait by an hour or two.
4. Seal and leave at room temperature for 10 to 24 hours. Shake or stir every few hours when you pass. By morning a clear, glossy syrup will have pooled at the bottom and the peels will look pale and dry.
5. Scrape everything into a bowl. To finish as a syrup, add 180 ml / 6 oz warm water, stir until the sugar dissolves, strain out the peels, bottle, date. To finish as a punch shrub, Difford's way, add 180 ml / 6 oz fresh lemon juice instead and shake until the sugar dissolves; the peels can go into the punch bowl.
6. Refrigerate. Use the water version within a week and the juice version within 4 days.

For the vacuum-bag variation Jeffrey Morgenthaler uses, muddle peels and sugar, seal in a vacuum bag, and leave at room temperature for 6 to 12 hours. The vacuum pulls the oil out faster and the bag keeps the aroma in.

Using it

• Punch: this is where it was born. Difford's quotes the old rhyme of one sour, two sweet, three strong, four weak; the shrub is your sour and sweet in one jar. For a bowl of 24 small servings: the four-lemon shrub, 750 ml of rum or cognac, 1 liter of cold water or black tea, a block of ice, and grated nutmeg. Let it stand on the ice 15 minutes before ladling.
• Sours: replace the simple syrup in a Whiskey Sour with an equal measure of oleo saccharum syrup. The drink reads as more lemon with no more acid, which lets you ease the juice back by 0.25 oz / 7.5 ml.
• Old Fashioned: a barspoon of oleo saccharum in place of the sugar cube gives you a drink that is already perfumed before the peel goes on.

Expressing a peel

A fresh peel, squeezed over the glass, is the fastest citrus technique in the bar and the easiest to do badly.

1. Cut a strip of peel about 2.5 inches (6 cm) long and 0.75 inch (2 cm) wide with the peeler, skin side out, as little pith as possible. Orange for the Old Fashioned, lemon for the Sazerac.
2. Hold it skin side toward the glass, 2 inches (5 cm) above the surface, between thumb and two fingers.
3. Fold it sharply once. You will see a small burst of oil in the light and smell it at once.
4. Rub the skin side around the rim if the drink wants it (the Old Fashioned does), then drop the peel in or lay it on the edge.
5. For the Sazerac, express the lemon peel over the drink and discard it. The glass carries absinthe and the drink carries bitters; the lemon oil on the surface is the whole garnish.

What can go wrong

• The syrup is bitter. Too much pith. Peel more lightly, or trim the strips with a paring knife before they go in the sugar.
• Nothing much happened overnight. Waxed fruit, or sugar too coarse to grip the peel. Scrub the fruit, use fine sugar, and muddle.
• The sugar set into a brick. Low humidity and no stirring. Add the water or juice; it will dissolve.
• Mold on day five. Water and fruit juice shorten the life of anything. Make what you will use in the week.
• The expressed peel does nothing. The fruit was old or the strip had no skin on it. A fresh lemon rolled firmly on the counter first gives up more oil.

Food safety

Oleo saccharum is sugar and fruit at room temperature for up to a day. That is safe for the maceration, because dry sugar holds the water activity too low for growth, and it stops being safe once the sugar is dissolved. Refrigerate after step 5, keep the jar clean, and use the dates above.

Sources

• Simon Difford, "Oleo saccharum: how to make citrus oil syrup" and "Punch: how to make, serve and enjoy", Difford's Guide.
• European Bartender School, "So, what is oleo saccharum?".
• Garden and Gun, "How to make oleo saccharum".