Why wine is white: white vinification
White vinification is a process that take place without maceration on the pomace. The stalks are removed before pressing the bunches as it hasn’t to contain tannins and the white wine has to be clear without parts in the surface.
The fermentation doesn’t foresees the contact with the air, to avoid the oxidation of the substances contained in the wine.
As a consequence, it highlights the fact that white wine is something delicate to produce and it have to be managed carefully. The air causes oxidation that compromise the clearness and the colour of the wine. Dark wines without a great bright yellow have been subjected to oxidation. The chemical reaction developed is similar to what happen when we cut the fruit leaving it in contact with the air. It becomes dark.
The temperature of fermentation of a white wine has to be controlled and kept at a temperature of 18-22°C. The fermenters, where it take place has to be provided with a double wall. In the space between the walls a refrigerating liquid flows. and it is able to keep the temperature stable.
White wine: how to stabilize the colour
White wine needs specific care in the cellar. The clarification of the liquid has the aim to tied together some substances that can create residual that can compromise the clearness. The organic substances used to clarify the liquid are casein, albumine and gelatine. Their function is to find the responsible of the colour and remove them, making them fall on the bottom. The filtering has the aim to hold some parts in the surface through sieves or electrostatic process. In the first case the wine filters thanks to a surface with small holes that hold all the microorganism responsible of the secondary fermentation. The second procedure foresees the electrostatic attraction of the parts like a magnet.
Why wine is white? The responsible substances
Flavonoids are yellow pigments in the white grapes. They are responsible of the white colour of the wines, in particular the Quercetin. It is a natural antioxidant. Chlorophyll is responsible of the photosynthetic process necessary to develop the vine. It participates to the transformation of carbon dioxide and water into sugar and oxygen.
Leucoanthocyanins and catechin are responsible as well of the colour of white wines, but they can polymerize, giving an astringent taste to the wine.
Threats to the white colour of the wine
Bacteria are dangerous microorganisms as they cause illness in the wine. In the production of white wine the producers pay attention to keep the acidity in the right levels. The freshness and the taste is given by the acidity that make the wine pleasant. Bacteria don’t attack a wine with a high degree of acidity. Oenologists correct the acidity adding tartaric or citric acid.
To keep the white colour perfectly brilliant it is possible to add sulfurous dioxide. It has an antiseptic, antioxidant action and it preserves the wine longer. The maximum doses are stabilized by the law with suitable regulation.
Last but not least, the presence of minerals in the wine influence in a relevant was the colour and the clearness. The copper, in particular, comes from anti parasitic given to the vine during its growth. The percentage of the other metals depends on the composition of the soil.