The 2012 ASHS Annual Conference

The chemical composition of grape berries has generally been accepted as the most important factor when determining harvest time.  The balance between sugar content, acidity, and phenolic ripeness are used to determine harvest times as both sugars and organic acids contribute to sensory quality, stability, and alcohol potential of wine. Developing a dynamic profile of these compounds facilitates harvest at optimal times to produce quality wines. Chemical composition changes during berry ripening have been studied extensively in Vitis vinifera cultivars, but little is known of the chemical composition of hybrid cold climate wine grape cultivars.  We sampled berries from eleven cold climate wine grape cultivars approximately every 10 days from August to October during the 2010 and 2011 growing season and assayed for soluble solids (°Brix), titratable acidity (TA), pH, and berry weight.  Concentrations of organic acids, sugars, and other metabolites were also measured to predict peak maturity time for the selected cultivars. Through the comparison of the concentration of sugars and acids to heat accumulation units such as Growing Degree Days (GDD), it was found that 1330 to 1500 GGD’s (Base 10 °C) are needed to fully ripen cold climate wine grapes to peak maturity.  Complete knowledge in the range of variation for these measurable components can be used to determine optimal harvest times of cold climate wine grape cultivars.