Our sense of sight is activated by light rays which pass through the crystalline lens and the vitrous body of the eye to the retina where light-sensitive cells called rods and cones transform them into electrical impulses. These are then carried by the optic nerve to the occipital lobe, the part of the brain responsible for the interpretation of visual stimuli.
The aim of the visual examination is to evaluate colour, clarity, fluidity and, for sparkling wines, effervescence.
Colour
Is examined by filling a tulip-shaped tasting glass about a third full and holding it against a white background at an oblique angle so that the surface of the wine assumes the shape of an ovular disc. Points to note are, besides the basic colour, the depth and the subtle differences in shade around the rim of the wine.
Clarity
Is judged by holding the glass between the eye and a subdued source of light against a dark background. This reveals the degree of transparency of the wine and the presence of any suspended particles which spoil its clarity.
Fluidity
To judge basic texture and viscosity, rotate the glass so that a light film of wine forms on the sides. When the glass is still again the liquid will slowly descend in "legs" or "tears". Numerous and very evident "legs" are an indication of a full-bodied wine.
Effervescence
Is judged by examining the bubbles (perlage) and the foam (mousse) which form in the glass immediately after the wine is poured. The first test of finesse in sparkling wines is the size and intensity and persistence of the carbon dioxide bubbles that rise from the bottom of the glass.