🍷 Flor

Flor is a film of yeasts that develops on the free surface of wine ageing in a cask. In Spanish the word means flower, and the Spanish dictionary also uses it for the film that wine forms at the top of the vessel. The film covers the wine and shields it from direct contact with the oxygen of the air.

Flor yeasts are strains of Saccharomyces cerevisiae. They rise to the surface and form the film when the wine has run out of fermentable sugars and nitrogen, and then switch to oxidative metabolism. They consume acetic acid, which lowers volatile acidity, and turn part of the ethanol into acetaldehyde; its by-products give sherry and similar wines their distinctive flavour.

Ageing under flor is called biological ageing. It is traditional in the Jerez area of Spain for sherry, in the Jura in France for vin jaune, in Sardinia for Vernaccia di Oristano and in the Tokaj region of Hungary for Szamorodni. Under the sherry rules the wine ages in oak butts of no more than 1,000 litres; fino ages only under flor and has 14 to 17 % vol. Because flor yeasts lower the alcohol, alcohol may be added during ageing to fino sold as liqueur wine to raise it again.

Fino from biological ageing shows aromas of green apple, nuts or yeast, like fresh bread dough. Amontillado first ages under flor and then without it, in contact with air, while palo cortado and oloroso age mainly or only oxidatively after the initial flor has disappeared.