A Comparative Study of the Phenolic and Technological Maturities of Red Grapes Grown in Lebanon

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 (R(2) = 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.