Which change occurs in wines that undergo biological aging under flor?

Wines that undergo biological aging under flor yeast experience several distinctive changes. Key among these is the production of acetaldehyde, which is a compound formed by the oxidative metabolism of ethanol by yeast. During this aging process, the flor yeast creates a protective layer on the wine's surface that allows for limited oxidation while simultaneously encouraging the development of unique flavors and aromas.

As a result of this process, the alcohol content tends to decrease slightly. This occurs because some alcohol is consumed by the flor yeast as part of its metabolic activity. Additionally, the presence of flor results in higher levels of acetaldehyde, contributing to the wine's characteristic nuttiness and complexity. The color of the wine does not typically intensify but rather remains neutral or pale due to the effects of the flor, which is also related to the minimal exposure to air.

These alterations are significant in producing the unique profiles of wines such as Fino and Manzanilla sherry, which are celebrated for their freshness and complexity derived from this style of aging.