Influencing grape colour

Growers can manipulate canopy structures to influence bunch development and berry sizing; producing a smaller berry will increase the skin to pulp ratio and produce a more intensely coloured wine.

Leaf removal at veraison is sometimes used to prevent further berry growth and thereby promote colour development in cool climates. However, too much sun, especially in hotter conditions, can decrease anthocyanin concentration.

High pH values can also alter the colour of anthocyanin solutions – responsible for red wine colour - by changing the structure of the anthocyanin molecule, which becomes bluer and therefore less desirable. 

The correct water balance is essential. Too much water results in higher potassium contents in the berry, increasing pH and reducing colour intensity. Severe moisture stress reduces colour. Colour can also be lost due to oxidation of phenolic compounds post-harvest, so it is important to ensure the fruit is kept cool prior to delivery.

Balanced nutrition, to ensure stress is minimized, helps to ensure a correct, natural balance of the different phenolic compounds in the bunch, thereby providing the desired wine colour.

Crop Nutrition and Grape Colour

Nitrogen

Increased nitrogen fertilization increases the anthocyanin content in the grape skin increasing the intensity of the colour of the wine. But high nitrogen levels can create vigorous growth and shading, increasing berry size, thereby reducing the ratio of skin to pulp

Potassium

Excessive potassium can increase grape pH which influences the anthocyanins, reducing the intensity of the red colouration. Potassium has a direct effect on the pH level in the must.

Boron

Foliar sprays with boron at the beginning of flowering and at the fruit set can increase anthocyanin contents, improving wine colour.

Other crop management practices Influencing grape colour

• Disease control is important, as various phenolic compounds are denatured under disease attack. 
• Botrytis causes the oxidation of a range of phenolic compounds during the winemaking process, leading to a brown colouration of white wines and a loss of colour in reds. 
• Growers should create an open canopy structure to minimize microclimates that favour pathogens and use appropriate fungicides when disease pressures dictate.