The prediction of maturity in plums for prune production

Abstract

The production of good quality prunes requires plums with a minimum of 26 per cent soluble solids content before dehydration. Maturity in plums was studied by determining specific gravity and soluble solids at weekly intervals over several weeks beginning at the approach of harvest. The regressions of soluble solids on specific gravity were linear and homogeneous over all crops and years studied. The proposed procedure for predicting soluble solids content is based on the determination of specific gravity and soluble solids at a pre-harvest sampling. Specific gravity can be determined on 5-lb samples in the field using a convenient and cheap hydrometer made from a wire basket attached to a sphere and graduated tube which floats in a drum of water. The prediction procedure uses the time rate of change of soluble solids and the mean regression of soluble solids on specific gravity. Analyses of the experimental data were summarized and used to estimate standard errors of predicted values for various numbers of 5-lb samples. The recommended prediction procedure is exemplified numerically and illustrated in a diagram.