University of California

Physical and chemical changes in French prunes during maturation in coastal valleys


L. L. Claypool
W. H. Dempsey
Paul Esau
M. W. Miller

Authors Affiliations

L. L. Claypool was Professor of Pomology and Pomologist in the Experiment Station, Davis; W. H. Dempsey was Associate Professor of Agriculture, Chico State College, California; Paul Esau was Laboratory Technician IV in the Experiment Station, Davis; M. W. Miller was Assistant Professor of Food Science and Technology and Assistant Food Technologist in the Experiment Station, Davis.

Publication Information

Hilgardia 33(8):311-318. DOI:10.3733/hilg.v33n08p311. November 1962.

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In 1951 and 1952, physical and chemical changes of French prunes during maturation on the tree were studied in the Sacramento Valley (Claypool and Kilbuck, 1956).7 In the warm interior valleys of California, French prunes usually remain firmly attached to the tree long after they attain maturity and, since shaking removes fruits of all maturities with about equal facility, a tree is completely harvested in one operation. For dried prunes of good quality, however, shaking must be delayed until all or nearly all fruits are mature.

In the cooler, coastal valleys attachment of French prunes to the tree usually becomes less firm as the fruits mature and therefore considerable numbers of ripe prunes may drop to the ground. Mature fruit is readily harvested by lightly shaking the main branches. Commercial harvesting operations involve two to four pickings, in contrast to the single picking in the interior valleys.

During 1956 and 1957, extensive tests on the effect of various harvesting procedures on quality of dried fruit were conducted in seven coastal valley orchards. In addition, fruits were tagged for study of physical and chemical changes during maturation. The latter study is reported here and compared with the previous study on interior valley prunes by (Claypool and Kilbuck (1956)).


Two orchards were selected for study: in 1956, one in the southern part of the

Literature Cited

Claypool L. L., Kilbuck John. Quality of dried French prunes. California Agriculture. 1955. 9(8):13-14.

Claypool L. L., Kilbuck John. The influence of maturity of interior valley French prunes on the yield and quality of the dried product. Proc. Amer. Soc. Hort. Sci. 1956. 68:77-85.

Claypool L. L., Miller M. W., Dempsey W. H., Esau Paul. The influence of harvesting procedures and storage on the quality of dried French prunes from coastal regions. Hilgardia. 1962. 33(8):319-48. DOI: 10.3733/hilg.v33n08p319 [CrossRef]

Esau Paul, Claypool L. L., Miller M. W., Dempsey W. H., Esau Paul. Procedures for conversion of color data from one system to another. Food Technology. 1958. 12:117

Maerz A., Rea Paul M. A dictionary of color. 1930. New York: McGraw-Hill Book Co., Inc.

Claypool L, Dempsey W, Esau P, Miller M. 1962. Physical and chemical changes in French prunes during maturation in coastal valleys. Hilgardia 33(8):311-318. DOI:10.3733/hilg.v33n08p311
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