What is a sour: the cocktail family built on acid balance

A sour in cocktail making is not a single recipe, but an entire family of cocktails that share the same principle of balance: the precise tension between a spirit, a citrus that provides acidity and a sweet touch that rounds off the whole. At STILLROOM we understand it as the mother formula of modern cocktail making, a pattern that gives rise to classics such as the whisky sour, the daiquiri, the margarita or the sidecar, and which in our laboratory we take into new dimensions with techniques such as clarification, lacto-fermentation or fat washing.

What the sour family is and how it works

Talking about “what is a sour” means looking beyond the glass. The sour family rests on a three-part structure that works like a tripod: a base spirit, a citrus that introduces acidity, and a sweetener that softens and unites both ends. That three-way relationship is the essence of the sour, and it is what allows personalities as different as a crystalline daiquiri or a silky clover club to emerge from the very same logic.

The classic sour formula boils down to a ratio many bartenders call the golden ratio: 2 parts spirit, 1 part citrus and 1 part sweet. Two, one, one. It is not an immovable law — at STILLROOM we are constantly adjusting it according to the real acidity of the citrus, the profile of the spirit and the type of sweetener we use — but it is the most reliable starting point for understanding how this balance is built. When that ratio is respected, the drink breathes: the alcohol does not bite, the acid does not scratch and the sweet does not cloy. It is a dynamic balance that translates, on the palate, into freshness, length and a final dryness that invites another sip.

The soul of the sour family is precisely that sweet-and-sour balance. Without the acidity of lemon, lime or grapefruit, the cocktail would be flat, heavy, one-dimensional. Without the sweet counterpoint — sugar, syrup, honey, cordial — the citrus would come across as harsh and astringent. What turns a sour into a great sour is the tension between both poles, a tightrope the bartender tightens or loosens with every specification. In our case, we work with citrus freshly squeezed to order and develop our own cordials and syrups — many of them fermented or vacuum-infused — to achieve nuances that go far beyond simple sweetness.

Then there is the component that does not appear in every recipe but defines the family’s most iconic texture: egg white or, in its plant-based version, aquafaba. When a sour includes egg white, we talk about a sour “with body”, a drink that gains a layer of silky foam and an enveloping mouthfeel that rounds off every edge. The technique for achieving this is the dry shake: shaking all the ingredients without ice first, so the protein emulsifies and forms that aerated structure, then adding ice and shaking again to chill and dilute. The result is a creaminess that has nothing to do with fat, but with protein emulsion, and that turns every sip into a tactile experience.

Essential cocktails of the sour family

When someone asks “which cocktails belong to the sour family?”, the answer starts with the classics every bartender knows and every drinker should try. But the beauty of it lies in seeing them for what they are: variations on the same pattern. Change the spirit, change the citrus, change the sweet, and what you get is a new drink with a personality of its own. This table gathers the most representative ones:

Classic sour	Spirit	Citrus	Sweet touch
Whisky sour	Bourbon or rye whiskey	Lemon juice	Simple syrup or sugar
Daiquiri	White rum	Lime juice	Sugar syrup
Margarita	Tequila or mezcal	Lime juice	Triple sec or agave syrup
Sidecar	Cognac or brandy	Lemon juice	Triple sec
Clover club	Gin	Lemon juice	Raspberry syrup or grenadine
Gimlet	Gin	Lime juice (or lime cordial)	Simple syrup or the cordial itself

Notice one detail: some include egg white — the whisky sour and the clover club are the classic examples — and others do not. The decision to foam or not to foam responds both to tradition and to the profile the bartender is after. At STILLROOM we serve the whisky sour with its crown of firm foam, worked with a dry shake and a dash of Angostura bitters on the surface that perfumes every sip. But we also offer a daiquiri without egg white, bright and clear, where what matters is the purity of the rum and the lime.

Anatomy of a sour: what each element does

Beyond the recipes, understanding a sour means grasping the function of each ingredient in the structure of the drink. It is not about adding things up, but about understanding how they interact in the glass and on the palate. This table breaks down that role:

Sour element	Function	Notes
Base spirit	Provides character, alcoholic structure and the main aromatic profile	Defines the cocktail’s identity. It can be a single spirit or a blend (split base). At STILLROOM we use techniques such as fat washing or infusions to modify its profile.
Citrus / acidity	Introduces freshness and vivacity and counteracts sweetness and alcoholic weight	Lemon, lime, grapefruit, yuzu… The real acidity varies according to ripeness and variety. We always measure to adjust the ratio. We also work with fermented or lacto-fermented citrus to add complexity without losing brightness.
Sweetener	Balances the acidity, rounds off the experience on the palate and can contribute secondary flavours	From simple syrup to honey, agave, sous-vide cordials, or fruit reductions. Its density and sweetening power determine the drink’s final texture.
Egg white / aquafaba (optional)	Generates foam, contributes a silky texture and softens the perception of acidity and alcohol	Emulsified with a dry shake. Aquafaba (chickpea cooking water) is the vegan alternative with almost identical results. In both cases we aim for a dense, stable layer.

The interesting thing is that this anatomy is, at the same time, a creative template. Any variation in one of the elements generates a new sour. Change the spirit, and the personality shifts; swap the lemon for grapefruit, and the acidity drops while bitter notes appear; replace the syrup with a fermented fig cordial, and the result is a completely different drink. That flexibility is what turns the sour family into the favourite canvas of signature cocktail making.

How we use the sour family at STILLROOM

At STILLROOM, the sour is not a mere academic exercise: it is our daily testing ground. We start from the classic formula but bring it onto our own turf by applying many of the advanced cocktail techniques we work with in the laboratory. Sometimes we clarify a sour so it is as transparent as glass while keeping all its flavour; other times we ferment the citrus to gain complexity, or infuse the spirit with seasonal herbs. The structure does not change: balance rules. But the results surprise.

When we make a Clover Club, for example, we respect the historic recipe — gin, lemon juice, raspberry syrup and egg white — but we make our own syrup with macerated raspberries and do a controlled dry shake to achieve a firm, silky pale-pink foam. If you come up to the bar and order a classic daiquiri, we serve it exactly as the canon dictates: quality white rum, freshly squeezed lime juice and just the right amount of sugar, shaken until the dilution is perfect. No flourishes, because a well-made daiquiri needs nothing more. And when we work on a margarita recipe, we do so with absolute respect for the boundary between the tequila, the lime and the triple sec, though we later allow ourselves to explore variations with mezcal, chapulín salt or stone-fruit cordials.

Our menu changes with the seasons, but the sour family is always present in one way or another. We work with non-traditional acids — fruit vinegars, whey, fermented citrus — that expand the concept of acidity without betraying the logic of the sour. And always, always, we measure, taste and adjust: because acid balance is not achieved with a fixed recipe, but with sensitivity and technique.

Three ideas for starting to explore sours

A textbook whisky sour

The ideal starting point for understanding the family. Use a full-bodied bourbon — some rye in the profile helps —, freshly squeezed lemon juice and a dense simple syrup. Add egg white, dry shake for fifteen seconds, add ice and shake again. Strain into a rocks glass over a large ice cube and top with a few drops of Angostura bitters on the foam. The result is creamy, just acidic enough, with the warmth of the whisky present throughout. Try adjusting the sweet ratio once you have it in front of you: that is how you start developing your own palate for balance.

A daiquiri as the minimal, perfect sour

If you want to see how simplicity, well executed, is unbeatable, the daiquiri is your sour. White rum, lime juice and sugar. Nothing else. The key here lies in the quality of the rum and the precision of the lime measure, because with so few elements any imbalance shows instantly. Shake with plenty of ice, fine-strain into a chilled glass and watch how a three-ingredient cocktail can be crystalline, bright and absolutely addictive. It is the sour in its most minimal expression and, at the same time, one of the most demanding to execute.

A house seasonal sour with egg white

This is where our obsession with seasonality comes in. Picture a sour built on a gin infused with fig leaves, organic lemon juice, a light fermented pear cordial and egg white. Shake it using the dry shake technique and serve it in a coupe glass. The foam comes out dense and long-lasting, the aroma is herbaceous and fruity, and the lemon’s acidity finds in the fermented pear a sweet, complex counterpoint that keeps shifting on the palate. These seasonal sours are what let us play with the calendar and with laboratory techniques without losing sight of the original formula.