Flor Film

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 

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Sherry wines are obtained from young wines, carefully selected soon after completing fermentation. These are typically fortified by adding vinous alcohol until they reach an alcohol content of 15-15.5°. They are subsequently transferred to oak barrels before being aged. In most sherries, wine aging occurs in the so-called solera and criaderas system under the flor film of yeast. Once alcoholic fermentation is finished, races of Saccharomyces cerevisiae that can grow on the surface of the wine switch from fermentative to oxidative (respiratory) metabolism. They spontaneously form a biofilm called flor on the wine surface. 

In Jerez, researchers have isolated four S. cerevisiae races or varieties two major races (beticus and montuliensis) and two minor ones cheresiensis and rouxii). The race beticus is faster in forming a flor film also, it is more abundant in the scales holding the younger wines. On the other hand, the race montuliensis prevails in the scales containing the oldest wine by virtue of its increased tolerance and production of acetaldehyde (Martinez et al. 1997a). 

The way the flor film forms, and its thickness, appearance and colour, depend on a variety of factors, mainly for the race S. cerevisiae. Especially influential among the cellar environmental conditions are temperature and moisture. The acceptable temperature range for this yeast race is 15-20°C (Marcilla et al. 1936) and the optimum value 15-17 °C. Ibeas et al. (1997) found a temperature of 22.5 °C to be the threshold above which the frequency of respiratory mutants (rho ), which are unable to form a flor film, rises fo a substantial extent. The relative humidity should be higher than 70%. 

Formation of the flor film is also affected by the ethanol content of the wine, the optimum value for which is 14.5-15.5 vol.% in fact, the film rarely forms above a 16.5 vol.% content. 

The formation of a flor film is the adaptive response of the yeasts to the extreme conditions prevailing in the medium, which include high concentrations of ethanol and... 

Metabolite concentrations in wine depend on the particular aging conditions, number of rows in the criaderas and solera system, number of rocios and volume extracted for bottles per year, ratio area of the flor film to volume of wine, climatic conditions of the cellar (temperature and relative humidity) and alcoholic concentration, in addition to the particular flor yeasts present. Below are described the most common changes observed during the biological aging of wine, whether related to yeast metabolism or otherwise. 

Wines aged under a flor film typically contain various compounds especially important among which are lactones. Thus, solerone (4-acetyl-y-butyrolactone) abounds mfino and Jura wines and has for years been deem one of the greatest contributors to their aroma profiles (Augustyn et al. 1971 Muller et al. 1973). However, subsequent studies have suggested that this lactone has no impact on wine aroma (Martin and Etievant 1991). 

Guijo, S., Mauricio, J.C., Salmon, J.M., Ortega, J.M. (1997). Determination of the relative ploidy in different Saccharomyces cerevisiae strains used for fermentation and flor film ageing of dry sherry-type wines. Yeast, 13,101-117. 

Valero, E., Millan, C., Ortega, J.M. (2002). Changes in the lipid composition of Saccharomyces cerevisiae race capensis (Gl) during alcoholic fermentation and flor film formation. Lebensm. Wiss. Technol, 35, 593-599. 

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