What is Lemon Juice?

Lemon juice is the citrus acid in whiskey sours, gin sours, Sidecars, and French 75s. As with lime, the cocktail ingredient is freshly squeezed juice: citric (and some malic) acid plus a volatile oil fraction from the fruit. Bottled lemon juice is pasteurized and typically from concentrate; it supplies acidity without the aroma of fresh fruit.

Recipes that specify lemon mean lemon. Substituting lime changes the aromatic family — sometimes into a legitimate variation (a whiskey drink with lime is closer to a Daisy or a rum-sour logic), often into a muddle of two templates.

Brighter and slightly rounder than lime, with less of lime’s green, sharp finish. The juice still oxidizes quickly once squeezed: ascorbic acid degrades, volatiles dissipate, and refrigerated leftover juice develops cooked, dull notes within a day or two.

The sour — spirit, citrus, sugar — is 19th-century structure. Lemon was the readily available citrus of the North Atlantic bar; lime was the citrus of the Caribbean and Mexico. That split still maps onto families: whiskey and cognac sours, the Tom Collins, and the French 75 on lemon; rum, tequila, and mezcal sours on lime.

Punch predates the short sour and used the same acid-and-sugar logic at bowl scale.

Squeeze to order. A working sour template is 2 oz spirit, ¾ oz lemon, and ¾ oz 1:1 simple syrup; adjust sugar to the fruit’s acidity and to any liqueur already in the drink. Strain out seeds and heavy pulp.

Do not hold squeezed lemon for a week. If you must batch, juice the same day you serve and keep it cold and covered.