Monitoring pH as grapes approach ripeness helps ensure optimum varietal character of the grapes at harvest. Regarding taste, wines with lower pH exhibit increased astringency and increased sourness. Knowledge of pH is also important for proper control of sulfur dioxide levels. Wines above pH 3.6 are also at risk of bacterial instability.
The following chart shows that desired levels of SO2 needed for bacterial control depend on the levels pH.
Monitoring titratable Acidity as grapes approach optimum ripeness helps ensure optimal varietal character at harvest. Wines produced from grapes where the overall acid levels have become too low are often bland, flat tasting and devoid of fruit character. Adjustment of titratable acidity is important to optimize extraction of flavor components prior to fermentation.
Titratable Acidity and Harvest
Titratable Acidity (g/L Tartaric Acid) Harvest Notes
≤4.0 Monitor earlier next year.
5.0 Monitor earlier next year.
6.0 OK to pick for Dessert Wines
6.5 OK to pick for Dessert Wines and for red still wines
7.0 OK to pick for Dessert Wines and for red and white wines
7.5, 8.0 and 8.5 OK to pick for all wines
≥9.0 OK to pick for sparkling whites
Physiological Ripeness of the Grape
The appearance of the grape when aroma and flavor become apparent is considered for the texture of the skin and pulp, and the color of the skin, stems and seeds. Unripe berries are firm; ripe berries are plump, juicy, and retain their shape when squeezed lightly; overripe berries begin to shrivel, and will remain depressed when squeezed. If the skin is still green, the tannins are said to be bitter and harsh. As the tannins continue to develop, the color of the seeds darken. Liquification of the stems occurs as they go from green to a woody brown. At this point the vine is finished with the clusters and is storing resources for next season.
Physiological Ripeness as reliable indicator of when grapes are ready to be harvested is discussed on Trending Now on Accuvin’s Homepage.
Finally, BALANCE: The ratio of sugar to titratable acidity has been recommended as one method of judging optimum ripeness. The most balanced red wines are considered to be 30 : 1 Brix to Titratable Acidity ratio. For white wines a good ratio is 25 : 1, and for sparkling wines, 20 : 1.