True aioli is garlic pounded to a smooth, sticky paste in a marble or stone mortar, then emulsified with olive oil added drop by drop — no egg yolk, no lemon at the outset, nothing but garlic, oil, salt, and the slow rotation of the pestle. This is the Provençal original, the sauce that predates mayonnaise by centuries, and the technique where the dish lives or dies is in the first thirty seconds: if the garlic paste is not perfectly smooth and cohesive before the first drop of oil falls, the emulsion will never form. Quality hierarchy: 1) Mortar-pounded aioli using Violet de Cadours or fresh hardneck garlic, Provençal extra-virgin olive oil, and nothing else — intensely aromatic, thick enough to hold a pestle upright, with a slow burn from raw allicin and a fruity olive finish. 2) Mortar aioli with a single egg yolk added for stability — slightly richer, more forgiving, still handmade. 3) Food-processor aioli — functional, but the blade heats the garlic and ruptures cells differently, producing a sharper, more acrid flavour that lacks the rounded sweetness of stone-ground paste. The emulsion science is the same as mayonnaise but more demanding. In egg-based emulsions, lecithin from the yolk acts as a powerful surfactant, stabilising oil droplets effortlessly. Without egg, the emulsifier is a combination of garlic's cellular mucilage and the mechanical energy of the pestle. The mortar's rough surface shears garlic cells, releasing sticky polysaccharides that coat oil droplets and prevent coalescence. This is why the mortar must be stone or ceramic — smooth stainless steel bowls cannot generate the necessary friction. The garlic matters at species level. Violet de Cadours, a French hardneck variety, offers moderate heat, deep sweetness, and a purple-streaked clove that pounds to an exceptionally sticky paste. Spanish Roja, another hardneck, provides earthier, more complex notes. Avoid Chinese softneck garlic — it is often harsh, overly sulphurous, and its lower sugar content produces a paste that tastes of nothing but burn. Fresh season garlic (late spring, early summer) is ideal: high moisture, mild heat, no green germ. If the clove has a green sprout at its centre, remove it — that germ is disproportionately bitter and will dominate the sauce. Begin with 4-6 cloves (roughly 20g) peeled and sprinkled with coarse sea salt — the salt acts as an abrasive, accelerating the breakdown. Pound in a circular motion, scraping the sides of the mortar, until you have an utterly smooth, wet paste with no visible fibre — 3 to 5 minutes of committed work. Now add oil: the first 50ml must go in drop by drop, with constant circular grinding. You will feel the resistance change as the emulsion forms — the pestle drags, the paste stiffens, the colour shifts from translucent grey-green to opaque ivory. Once the emulsion catches, you can increase the oil flow to a thin stream. Total oil: 200-250ml for 20g of garlic. If the sauce becomes too thick, a few drops of warm water (not lemon, not yet) will loosen it without breaking the emulsion. Season with lemon juice at the end, to taste. Sensory tests: the finished aioli should hold a firm peak on the pestle. It should smell intensely of garlic with a clean olive-oil backdrop — no metallic or acrid notes. The colour should be pale ivory to light gold. Taste should deliver garlic heat that builds slowly, followed by fruity oil sweetness, then a long peppery finish from the olive oil's polyphenols.
Temperature matters more than most cooks realise. All ingredients should be at room temperature — cold oil is more viscous and harder to emulsify in small quantities; cold garlic is firmer and resists breaking down in the mortar. The mortar itself should be at room temperature or slightly warm. Work in a stable environment: set the mortar on a damp towel to prevent it sliding. The ratio is roughly 50ml oil per large clove of garlic. Exceed this and the garlic's emulsifying capacity is overwhelmed — the sauce will thin, then break. If you need more volume, add another clove rather than more oil. Pounding technique: use the pestle in a firm circular grinding motion, pressing the paste against the sides and bottom of the mortar. Do not bash or stamp — you are grinding, not hammering. The motion should be continuous and rhythmic. Speed is less important than consistency. If the aioli breaks — and it will break at some point in every cook's career — do not discard it. Take a fresh clove of garlic, pound it to paste, and beat the broken sauce into the new paste, teaspoon by teaspoon. It will re-emulsify. This rescue is identical in principle to restarting a broken mayonnaise with a fresh yolk. Serve aioli at room temperature, around 18-22°C/64-72°F. If the emulsion breaks, a common cause is oil that was too cold — straight from the refrigerator at 4°C/39°F. Both garlic paste and oil should be at room temperature before you begin.
In Provence, grand aioli is a complete meal: the sauce served at the centre of the table surrounded by poached salt cod, boiled potatoes, steamed vegetables, hard-boiled eggs, and snails. The sauce is the star; everything else is the vehicle. For a Catalan allioli, omit even the salt until the end and use a wooden mortar — the result is even more intensely garlic-forward. A single anchovy fillet pounded into the garlic base before adding oil creates a deeper, more savoury aioli without any identifiable fish flavour — the glutamates from the anchovy amplify the garlic's natural umami. Saffron aioli (rouille) follows the same method but adds soaked saffron threads and a pinch of cayenne to the garlic paste before emulsifying — this is the traditional accompaniment to bouillabaisse. For service in a professional kitchen, make the aioli slightly thicker than desired and thin to final consistency with warm water just before plating — this gives you a stable holding sauce that can be adjusted to the perfect nappé consistency at the last moment.
Adding oil too quickly at the start — the single most common failure. Without egg yolk as emulsifier, the garlic paste can only absorb oil in tiny increments until the emulsion is established. Dumping even a tablespoon before the emulsion catches will produce a greasy, separated puddle. Using a blender or food processor and calling the result aioli — the blade generates heat through friction, converting allicin into harsher sulphur compounds, and the violent shearing produces a sauce with a tinny, metallic bite entirely absent from mortar-made versions. Using old or sprouting garlic — the green germ is intensely bitter and will ruin the flavour balance. Not pounding the garlic thoroughly enough before adding oil — visible garlic fibre means insufficient cellular breakdown, which means insufficient emulsifier released. Using bland, refined olive oil — aioli is essentially flavoured oil, so the oil must be worth tasting on its own. Adding lemon juice too early, which thins the emulsion before it is stable enough to absorb the acid without breaking.