Flor yeasts

Flor sherry aldehydes Unknown Unknown Flor yeast... 

Some wines such us Sherry (Spain), Vemaccia (Italy), and Jura yellow (France) are developed under oxidative conditions, utilizing yeasts known as Flor-yeast. These yeasts belong to the S. cerevisiae var. prosto-serdovii which aid in the development of certain specific sensory characteristics (Fatichenti et al., 1983a,b). Studies were conducted with flor-yeast... 

Several studies have been aimed at elucidating the relationship between the activity of particular flor yeast enzymes during velum production, both in lab-scale and under winery conditions. For example, studies on the activity of alcohol and aldehyde dehydrogenase have... 

During the biological aging of sherry, the concentration of ethanol decreases because of its consumption by flor yeast. Its respiration via the tricarboxylic acid pathway (Suarez-Lepez and Inigo-Leal, 2004) provides the main source of carbon and energy. Acetaldehyde is the main organic byproduct of ethanol metabolism, but other volatile compounds, notably acetic acid, butanediol, diacetyl, and acetoin, can also be formed. In addition,... 

Besides the use of amino acids as a nitrogen source, flor yeast may use these compounds to balance the oxidation-reduction potential under conditions of restricted oxygen availability. This can be achieved by releasing amino acids into the medium to restore the intracellular redox balance by oxidation of excess NADH (Mauricio et ah, 2001a,b Moreno-Arribas and Polo, 2005 Valero et ah, 2003). 

Blandino, A., Caro, I., and Cantero, D. (1997). Comparative study of alcohol dehydrogenase activity in flor yeast extracts. Biotechnol. Lett. 19, 651-654. 

Esteve-Zarzoso, B., Femandez-Espinar, M. T., and Querol, A. (2004). Authentication and identification of Saccharomyces cerevisiae flor yeast races involved in sherry ageing. Anton. Leeuw. Int. J. G. 85,151-158. 

Martinez, P., Codon, A. C., Perez, L., and Benitez, T. (1995). Physiological and molecular characterization of flor yeasts polymorphism of flor yeast populations. Yeast 11, 1399-1411. 

Mauricio, J. C., Moreno, J. J., and Ortega, J. M. (1997). In vitro specific activities of alcohol and aldehyde dehydrogenases from two flor yeasts during controlled wine aging.. Agric. Food Chem. 45,1967-1971. 

In the traditional Spanish flor process, the flor yeasts grow on the surface of wine in partially filled barrels, that is, in contact with air. The yeast colonies growing on the surface often resemble flowers in shape and give the process its name ( flor being the Spanish word for flower). 

The shermat should be a clean, neutral white wine. The ethanol content of the shermat can be 12-16.5 percent. However, 14.5 percent is a good level. Lower ethanol wines are susceptible to acetification. At the upper limits, the flor yeasts do not grow or grow very slowly. The pH can be from 2.9 to 3.6. We have found 3.2 is a good average. At a lower pH, yeast develops very slowly. At over 3.4 pH, there is a risk of the growth of lactic acid bacteria. 

The shermat is inoculated with an active culture of Saccharomyces beticus or similar flor yeast. [As of 1981, this will be classified as S. cerevisiae, Ed.] Dehydrated flor yeast is not acclimated to ethanol and must be fermented to produce a yeast that will grow in 14.5 percent ethanol media. 

The combination of oxygen and flor yeast in a suitable shermat results in yeast growth and production of acetaldehyde. The wine passes through many taste and aroma phases during this process. The process is very flexible and can be used to produce anything from a pleasantly aromatic wine at 200 mg/L aldehyde to a strongly flavored flor sherry at 700 mg/L aldehyde to an intensely flavored flor with a long aftertaste at 1000 mg/L aldehyde. 

Castor and Archer (13) investigated the amino acid requirements of flor yeast growth and suggested more work should be done since the experiments were not conclusive. This is still true. Submerged flor production is still an art. All of the necessary conditions for a successful flor fermentation are not known, or at least they have not been published. We still have failures for unknown reasons. 

Flor Yeast Saccharomyces beticus, Appl. Microbiol. 1957, 5, 55-60. 

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