Water in Grape Berry and Wine

Water represents 90% of the harvest weight in a crop. When the crop is harvested and pressed, water can represent from 75-85% of the must and in the case of wine, can represent between 65-94%, depending on wine sugar content.
Vine growth and grape berry development are closely related to water availability in the soil and water availability in the soil is related to the Soil Texture and Water Holding Capacity.
Water Deficit:

• water deficit generally leads to smaller berries since it inhibits both cell division and, especially, cell expansion.
• timing of the water deficit is clearly important in order to determine fruit and wine composition
• irrigation can provide a means to manipulate wine sensory characteristics in the vineyard
• water deficit has a less pronounced effect on sugar accumulation than on berry growth
• when water deficit occurs post-véraison, fruit sugar is often reduced rather than being improved
• malate decrease occurs primarily when water deficit occurs before véraison

The Role of the Xylem and the Phloem

• The Grape Berry Circulatory System relies on the xylem and the phloem
• water influx into fruits occurs via both the xylem and phloem
• most of the berry volume gain before véraison is due to water import from the xylem
• most of the post-véraison gain is due to water import from the phloem
• at véraison, there is a substantial reduction in the proportion of water that is transported to the berry through the xylem compared to the phloem
• sugar accumulation in the grape berry is associated with the shift from xylem to phloem water transport at the transient onset of berry ripening
• the shift from xylem to phloem function at véraison would prevent a substantial water or solute backflow from the fruit to the plant

References:
1. Text and illustration from: Carlos Conde, Paulo Silva, Natacha Fontes, Alberto C. P. Dias, Rui M. Tavares, Maria J. Sousa, Alice Agasse, Serge Delrot, Hernâni Gerós, Biochemical changes throughout Grape Berry development and fruit and wine quality, Food, 1(1), 1-22 ©2007 Global Science Books.