Wine Arcana

Concept

Flor

Also known as Velo de flor

Flor is a film of yeast that develops on the surface of certain wines during maturation. It drives the biological ageing associated with fino and manzanilla Sherry, while related yeast veils develop in wines such as the Jura's vin jaune. The film changes both the wine's exposure to oxygen and its chemical composition.

The principal organisms are specialized strains of Saccharomyces cerevisiae, the species also widely responsible for alcoholic fermentation. Their ability to persist at the wine's surface allows a further phase of metabolism after most fermentable sugar has been consumed.

Life at the surface

Flor yeasts can switch from fermenting sugar to using oxygen to metabolize ethanol and other available compounds. Changes in their cell surfaces help cells aggregate and form a floating biofilm, a community growing together at the boundary between wine and air. Access to oxygen makes that position valuable to the yeast.1. Jean-Luc Legras et al., “Flor Yeast: New Perspectives Beyond Wine Aging,” 2016, introduction and discussion of biofilm formation and metabolism.

Partly filled casks provide the necessary wine surface and airspace. The yeast consumes oxygen there, helping limit its availability to the bulk wine. Biological ageing consequently combines aerobic microbial activity at the surface with protection of the liquid below from extensive oxidation.

The metabolism changes flavour. Acetaldehyde accumulates as the yeast uses ethanol, contributing the pungent aroma associated with biologically aged Sherry. Glycerol and acetic acid can decline as they are consumed.1. Jean-Luc Legras et al., “Flor Yeast: New Perspectives Beyond Wine Aging,” 2016, introduction and discussion of biofilm formation and metabolism.2. Consejo Regulador, “Ageing,” biological ageing and cask-management sections, accessed 14 September 2026.

Maintaining the veil

Alcohol strength, temperature, nutrients, and oxygen availability influence whether the film develops and remains active. In the traditional Sherry fortification route, producers bring wines intended for biological ageing to about 15% alcohol. A higher addition, taking the wine to around 17% or above, prevents sustained flor development under those cellar conditions and directs the wine toward oxidative maturation.3. Consejo Regulador, “Fortification,” accessed 14 September 2026; conventional cellar practice, not a universal microbial alcohol limit.

These conditions also explain the importance of cellar management. A biologically ageing wine must retain headspace, and the yeast needs a continuing supply of nutrients. Refreshment with younger wine in a solera helps sustain that activity. Cask handling aims to mix the incoming wine while limiting disturbance of the surface film and the sediment below.

When flor weakens or disappears, the wine's exposure to oxygen changes. Amontillado's passage from biological to oxidative ageing preserves the chemical effects of its earlier time under yeast while adding a subsequent course of development.

Variation between cellars and wines

In the Jura, the surface film is commonly called the voile. Vin jaune ages in partly filled casks without the repeated replenishment characteristic of a Sherry solera. Its unfortified base wine and static maturation create a different environment for the yeast.

A study of Savagnin wines from two Jura cellars found substantial variation in veil colour and structure, although S. cerevisiae predominated. Different strains could share a veil, and the dominant strain could change during ageing. The same strain also produced different-looking films in different wines.4. Vanessa David-Vaizant and Hervé Alexandre, “Flor Yeast Diversity and Dynamics in Biologically Aged Wines,” 2018, results and discussion. The visible film therefore reflects both the organisms present and the liquid in which they grow.

The researchers occasionally detected other species, including Brettanomyces. A surface film's appearance alone cannot identify its organisms or establish that the wine is developing as intended. Tasting, chemical analysis, and microbial identification supply different information about its condition.

Sources