Influence of Artificial Shading of Vineyards on the Concentration of Sugar and Organic Acid in Grapes

Abstract

Vines of Vitis vinifera L., varieties `Pinot noir' `White Riesling', and `Sauvignon blanc', were covered from approximately mid-July to mid-September with one of two types of plastic Saran shade material which reduced the total solar radiation to either 30 or 21% of full sunlight.

Reduced light delayed fruit maturation 1 to 5 weeks. The total accumulated calories of solar and sky radiation required for the maturation of fruits from `White Riesling' and `Sauvignon blanc' vines grown under 30% sun averaged 16% and 20% less, respectively, than the energy required for the maturation of grapes grown in full sunlight. Total acidity and concentration of malates in mature `Sauvignon blanc' fruits grown under 30% sun were approximately 20 and 13% greater, respectively, than in fruits of similar maturity from vines grown under full sun. The concentration of tartrate of 21 and 30% sun fruits were nearly equal, whereas the concentration of malate was slightly higher in the 21% sun fruits. The average fresh weights of berries from 30% and from 100% sun vines were approximately the same; however, average fresh weight of berries was usually slightly less for 21% sun vines than for vines receiving higher light intensities. The maturation and composition of `Sauvignon blanc' fruits from vines covered 2 weeks before vérasion were not significantly different from fruits of vines covered at vérasion.