Ripening changes in chemical composition of the 4 winegrape cultivars were investigated during 3 years from 1979 to 1981. The cultivars tested were ‘Riesling’, ‘Chardonnay’, ‘Koshu’ and ‘Riesling Lion’, cultivated on the experimental vineyard of Yamanashi University.<br>The results are summarized as follows:<br>1. The berry weights of ‘Riesling’, ‘Chardonnay’ and ‘Riesling Lion’ reached the maxima in mid-September, and were 1.6g, 1.9g, and 3.4g, respectively. The berry weight of ‘Koshu’, however, reached the maximum of 4.0g in mid-October. The berries of ‘Koshu’ and ‘Riesling Lion’ were heavier than those of ‘Riesling’ and ‘Chardonnay’.<br>2. The 4 cultivars showed respective changes in pH of the musts during ripening. At full maturity, the pH of ‘Riesling’ and ‘Chardonnay’ musts were 3.5, that of ‘Riesling Lion’ must 3.3, and ‘Koshu’ must 3.2.<br>3. In ‘Riesling’, ‘Chardonnay’ and ‘Riesling Lion’, the °Brix was 15% in early September and 18 to 19% in late September. In ‘Koshu’, a late cultivar, the °Brix was 15% in late September and 17% in mid-October.<br>4. The highest titratable acidity was observed in late July in ‘Riesling’ and ‘Chardonnay’, while in early August in ‘Koshu’ and ‘Riesling Lion’. At the harvest time, the value was more than 0.70g/100ml in ‘Chardonnay’, ‘Koshu’ and ‘Riesling Lion’, and 0.60g/100ml in ‘Riesling’.<br>5. The °Brix-acid ratios of the 4 cultivars at full maturity were more than 20 in the Kofu Area. The time to give full maturity, the °Brix, titratable acidity (g/ 100ml), and the ratio were mid-September, 17.3, 0.76, and 22.8 for ‘Riesling’; mid-September, 17.7, 0.88, and 20.1 for ‘Chardonnay’; early October, 17.6, 0.84, and 20.2 for ‘Koshu’; late September, 18.4, 0.81, and 22.7 for ‘Riesling Lion’, respectively.<br>6. At full maturity, the tartaric-malic acid ratios and the glucose-fructose ratios were 1.5 and 0.9 for ‘Riesling’, 2.0 and 0.9 for ‘Koshu’, 1.1 and 1.0 for ‘Chardonnay’, and 1.6 and 1.0 for ‘Riesling Lion’, respectively.<br>7. Several viticultural characteristics of the 4 cultivars were as follows. ‘Riesling’ suffered from white rot and ripe rot frequently, and the grapes were closely clustered and easily cracked. The whole ripening period was short and the heat accumulation for the optimum maturity was low, so it is a cultivar adapted to cultivation in cool areas. ‘Chardonnay’ seldom suffered from any disease and was a good producer. So this cultivar was easy to cultivate and can be adapted in cool areas. Both ‘Koshu’ and ‘Riesling Lion’ were easy to cultivate, although sometimes suffered from downy mildew. ‘Riesling Lion’ needed regulation of cropload.<br>8. The sensory impressions of the aftertastes of the wines made from the grapes of 4 cultivars were as follows. The ‘Riesling’ wine lacked vinous aroma and body. The ‘Chardonnay’ wine was fruity and harmonious with body and the best among the 4 wines. The ‘Koshu’ wine had a fresh and fruity aroma. The ‘Riesling Lion’ wine had a neutral flavor, and was slightly watery in taste.