Influencing wine 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 colored wine.
Leaf removal at veraison is sometimes used to prevent further berry growth and thereby promote color development in cool climates. However, too much sun, especially in hotter conditions, can decrease anthocyanin concentration.
High pH values can also alter the color of anthocyanin solutions – responsible for red wine color - 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 color intensity. Severe moisture stress reduces color. Color can also be lost due to oxidation of phenolic compounds post-harvest, so it is important to ensure 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 color.
Crop Nutrition and Wine Grape Colour
Nitrogen
Increased nitrogen fertilization increases the anthocyanin content in the grape skin increasing the intensity of the color 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 coloration. Potassium has a direct effect on the pH level in the must.
Boron
Foliar sprays with boron at the beginning of flowering and at fruit set can increase anthocyanin contents, improving wine color.
Other Crop Management Practices Influencing Wine Grape Color
- 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 wine making process, leading to brown coloration of white wines and a loss of color in reds.
- Growers should create an open canopy structure to minimize microclimates that favour pathogens and use appropriate fungicides when disease pressures dictate.
