In order to make wine, grapes must undergo alcoholic fermentation. In the case of red wine, the vessel used for fermentation, dependent upon winemaker preference, will also contain the skins, seeds and stems. During fermentation, yeast produce carbon dioxide, this carbon dioxide causes grape solids to rise creating what is referred to as a cap. The cap can present a number of risks, a combination of acetic bacteria, the warmth of fermentation and oxygen could easily convert a vat to vinegar. For this reason, winemakers must manage the cap. Cap management also forms part of the winemakers desired stylistic preference. Tannins, anthocyanins and flavour compounds, all essential to a wines character, are found in large quantities in grape skins and so varying methods of cap management will greatly alter a finished wine. Fail at cap management, and you may well have failed the wine.