Genoa, Liguria. Documented in Genovese recipe books from the mid-19th century, though the technique of grinding herbs, oil and cheese in a mortar is ancient Mediterranean. DOP status granted 2005.
Pesto made in a marble mortar with a wooden pestle — the only authentic method. The mechanical action of a blender oxidises the basil through heat and speed, turning the sauce brown and bitter within minutes. Mortaio work is slow, circular, and cold: the marble stays cool, the pestle bruises rather than cuts, and the oil emulsifies gradually into a pale, vivid green paste that smells of the herb at its peak.
Cold mortaio work preserves the volatile aromatic compounds in basil that heat and oxidation destroy. The finished pesto is grassy, sweet, faintly anise-like, with a clean pine-nut richness and the salty sharpness of aged cheese — nothing like the cooked, brown paste from a blender.
The mortar-and-pestle technique matters because basil cells are torn rather than sliced. Blades cause heat through friction and cut cells in ways that release oxidising enzymes immediately. The sequence — garlic and coarse salt first (the salt acts as abrasive), then pine nuts, then basil leaves in batches, then cheese, then oil in a thin stream — controls emulsification and prevents premature breakdown. DOP Genovese basil (Ocimum basilicum var. Genovese) is small-leafed with lower essential oil content than garden basil; this is not interchangeable.
Work in small batches and rest between them if the mortar warms. A drop of cold water on the basil leaves before bruising helps preserve colour. The Ligurian ratio: 50g basil, 2 garlic cloves, 30g pine nuts, 60g Parmigiano, 10g Pecorino Sardo, 80ml Ligurian extra-virgin oil. The Pecorino is non-negotiable — it brings the mineral sharpness that balances the fat.
Using a blender or food processor — produces oxidised, bitter paste. Using mature, large-leafed basil — too pungent. Adding oil too fast before the paste forms. Over-working once oil is added — the emulsion breaks. Using fine salt instead of coarse — no abrasive action. Refrigerating finished pesto — cold solidifies the oil and dulls the flavour.
Marcella Hazan, Essentials of Classic Italian Cooking; Giorgio Locatelli, Made in Italy