Sampling Vidal Blanc Grapes. II. Sampling for Precise Estimates of Soluble Solids and Titratable Acidity of Juice

Abstract

For two production seasons variance estimates of random components of vines, shoots, and berries were calculated for soluble solids and titratable acidity of Vidal blanc grapes. Variance estimates were then used to devise sampling strategies which would detect a specified difference at a selected level of Type I error. Graphs illustrate sampling schemes which achieved the desired level of precision. For example, a soluble solids difference of 1% could be detected by randomly selecting four berries from each of ten shoots on each of 36 vines (averaging two years' data). Soluble solids of the five apical berries from a cluster was not equivalent to soluble solids of the whole cluster. While on the average apical berries were 0.3% lower in soluble solids than the whole cluster, individually the apical berry samples were as much as 9.8% lower and 3.6% higher in soluble solids than whole clusters. These data differ from results in Concord and indicate that sampling schemes devised for one grape cultivar are not necessarily applicable to others.