Wine flower is caused by

Wine flower is caused by yeast.
It is like a thin layer of bacteria has formed on your wine. Winemakers refer to this as flowers or flowers of wine. It slowly degrades the wine and ferments some of the alcohol in the wine.
Flor in winemaking is a film of yeast on the surface of the wine, important in the manufacture of some styles of sherry. The flor is formed naturally under certain winemaking conditions, from indigenous yeasts found in the region of Andalucía in southern Spain.