Flor in winemaking, is a film of yeast on the surface of wine, important in the manufacture of some styles of sherry. The flor is formed naturally under certain winemaking conditions, from indigenous yeasts found in the region of Andalucía in southern Spain. Normally in winemaking, it is essential to keep young wines away from exposure to air by sealing them in airtight barrels, to avoid contamination by bacteria and yeasts that tend to spoil it. However, in the manufacture of sherries, the slightly porous oak barrels are deliberately filled only about five-sixths full with the young wine, leaving "the space of two fists" empty to allow the flor yeast to take form and the bung is not completely sealed. The flor favors cooler climates and higher humidity, so the sherries produced in the coastal Sanlúcar de Barrameda and El Puerto de Santa María have a thicker cap of flor than those produced inland in Jerez. The yeast gives the resulting sherry its distinctive fresh taste, with residual flavors of fresh bread. Depending on the development of the wine, it may be aged entirely under the veil of flor to produce a fino or manzanilla sherry, or it may be fortified to limit the growth of flor and undergo oxidative aging to produce an amontillado or oloroso sherry.
