Designation (span. rancio = rancid) for wines from hot wine-growing regions which have undergone oxidative ageing with simultaneous exposure to heat. However, the temperature is lower than in the related process of madeiraization, so that the notes of nuts and rancid butter tend to predominate in rancio, while a caramel note dominates in Madeira. Rancio is also commonly used for the typical wine flavour of candied fruit, nuts and rancid butter. The rancio tone is produced by oxidation of fatty acids and formation of butyric acids. Other Rancio style wines are Banyuls, Fondillón, Maury, Rasteau and Rivesaltes. Cognacs matured in barrels for a very long time also take on a rancio tone (Rancio charentais). In French Vin Jaune and Italian Vin Santo, the term rancio is sometimes used incorrectly. Related terms are firned, madeirised, oxidised, rahnrancid and rancid.
In the Spanish region of Catalonia, rancio is a speciality that is produced in numerous variations from dry to sweet. Here, mainly white wines are oxidized by the targeted action of oxygen through fermentation tank openings that are only loosely closed. The wine is sprayed to an alcohol content of 18 to 19% vol. and then matured in oak barrels or pear-shaped bombonas (glass balloons), whereby the containers are often deliberately exposed to the heat or extreme temperature fluctuations in warehouses that are hot during the day and cool at night. The high alcohol content prevents the development of Acetobacter (acetic acid bacteria). After several years of ripening, a Rancio is blended with Mistela (fortified must) or Arrope (grape juice concentrate) to achieve the desired degree of sweetness.