Abstract
Grape harvest date is determined according to the technological and phenolic maturities. These parameters were calculated for different red grape (Vitis vinifera L.) varieties (Cabernet Sauvignon, Merlot, Syrah, Cabernet Franc) over four years (2008, 2009, 2010, and 2011) (642 samples). Titratable acidity and sugar content of the grapes were used to determine the technological maturity, whereas Glories (1 and 2) and ITV (Institut Technique de la Vigne et du Vin) methods were used to monitor their phenolic maturity. The ITV method allows the monitoring of phenolic maturity by the quantification of total polyphenol index and anthocyanins, while the Glories method enables the quantitative evolution of extractable anthocyanins and tannins of the grapes. A correlation was shown between the harvest dates obtained by both ITV and Glories (R2 = 0.7 – 0.93). Phenolic maturity of grapes can, therefore, be optimized by the application of both ITV and Glories. Similarly, a correlation was observed between technological and phenolic harvest dates. The effect of climate on the phenolic content of grapes was also studied. The highest temperatures (up to 25 °C) accompanied by the lowest rainfall (null value), induced the maximal concentration of polyphenols in grapes. Thermal and water stresses were also shown to enhance the grapes’ polyphenolic production.
Highlights
In the winemaking industry, wine quality is largely influenced by grape harvest time, which is defined by many parameters such as the technological and phenolic maturity of the grapes.Technological maturity is characterized by the sugar content, which determines the potential alcohol content of the future wine, as well as the titratable acidity and pH of grapes must, which in turn contributes to the color and quality of the wine
The Total polyphenol index (TPI) peaks were reached at the same time than those of anthocyanin content
Technological maturity of 642 samples was determined by the measurement of the titratable maturity
Summary
Wine quality is largely influenced by grape harvest time, which is defined by many parameters such as the technological and phenolic maturity of the grapes. Technological maturity is characterized by the sugar content, which determines the potential alcohol content of the future wine, as well as the titratable acidity and pH of grapes must, which in turn contributes to the color and quality of the wine. The sugar content is usually determined by a refractometer to measure the refractive index or by total soluble solids (Degrees Brix) using density studies. The concentrations of anthocyanins and tannins, which are the most abundant polyphenols in red grapes, are good indicators of phenolic maturity since they accumulate in the grape skins during the ripening process.
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