Prediction of Acid Concentration in Wine and Table Grape Berries from Air Temperature

To develop equations to predict the titratable acidity of grape berries at harvest from air temperature, we analyzed several years of datasets on wine grapes grown in experimental vineyards in seven prefectures and of table grapes grown in 37 prefectures in Japan. Although the number of days from the full-flowering date to harvest date varied with the cultivar, the temperature throughout the period of 40 to 50 days before the harvest date was the most strongly correlated with the titratable acidity of all tested cultivars. The titratable acidity at the harvest date of the wine grape cultivars decreased as the mean temperature of the period increased as did that of the table grape cultivars, although the latter did not decrease much above 24°C. The titratable acidity of the wine grape cultivars showed good linear regression with the mean temperature from 60 to 99 DAF (days after full-flowering) in ‘Chardonnay’, from 65 to 109 DAF in ‘Monde Briller’, and from 35 to 84 DAF in ‘Colline Verte’. That of table grape cultivars grown in cold regions showed good quadratic regression with the mean temperature from 50 to 92 DAF in ‘Kyoho’, from 46 to 91 DAF in ‘Pione’, and from 52 to 93 DAF in ‘Suzuka’. The titratable acidity of table grape cultivars grown in warm regions was estimated to be about 0.5 g/100 mL. These regression equations can be used to select cultivars to plant and to identify suitable regions for each cultivar, as well as to estimate changes in acid concentration under global warming. We also determined the relationship between the rate of acid reduction of the wine grape cultivars and temperature from serial measurements of titratable acidity to allow growers to predict the change in titratable acidity.