Chapter 3 – Yeasts Used in Biologically Aged Wines

Most biologically aged wines are fortified to a strength of at least 16% alcohol and then aged under a thick, rough, white layer of yeast known as flor , formed by yeasts belonging to the genus Saccharomyces . The formation of this film depends on numerous factors, including the presence of proteins known as adhesins on the cell surface. The main adhesin involved in flor formation is encoded by Flo11 , and the mechanisms regulating its expression are complex. These proteins are highly hydrophobic and are responsible for cell-cell adhesion and the formation of a flor that becomes progressively thicker and floats on the surface of the wine. Thanks to this flor , the yeasts that participate in biological aging are highly resistant to alcohol, acetaldehyde, oxidative stress, and other hostile conditions, and most of them remain metabolically active throughout the aging process. As the must used to make biologically aged wines is fortified when all the sugars have been fermented, flor yeasts have an exclusively aerobic metabolism. The combination of the flor and the oxidative metabolism of the yeasts that it comprises creates a reducing environment that determines many of the organoleptic characteristics of the resulting wine. The aging of wine under a flor of yeasts followed by the use of a unique dynamic aging system known as soleras and criaderas results in the production of excellent wines.