Phenolic Ripeness and Sugar Ripeness

Many factors influence the chemical composition of grapes and the quality of wines including:

• maturity stage
• genetic makeup
• climatic conditions
• management practices

To make a high quality wine, grapes must contain an adequate amount of sugars and acids, but also balanced levels of phenols. Sugar concentration is an indicator of berry maturity (“sugar ripeness”) and determines the ethanol content of the wine.
Changes in tannin content are used by the growers to control harvest, and this process is called “phenolic ripeness”. Sugar ripeness may affect phenolic ripeness because the expression of several enzymes of the phenylpropanoid pathway may be controlled by sugars.
Phenolic ripeness allows the selection of flavoured grapes and avoids the unpleasant unripe tastes in the wine.
Factors affecting phenolic ripeness:

• increased sunlight and moderate fertility support vine growth and cluster formation and lead to an increased formation of secondary plant products, including phenolics
• quercetin is an excellent indicator of sunlight available to the development of grape clusters
• ample but not excessive moisture
• adequate, but not excessive fertility will also result in higher concentrations of phenolics and tannins in red wine grapes
• nitrogen, present in the soil as nitrite and nitrate, affects polyophenols content and, consequently, the wine taste and flavor
• disease pressures can result in reduced berry quality, leading to reduced phenolic content over time in harvested grapes
• the enzyme laccase produced by B. cinerea can degrade complex polyphenols and thus modify wine flavour and colour
• esca disease results in significant changes in the phenolic composition of grapevine leaves

References:
1. 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.