University of California

The influence of harvesting procedures and storage on the quality of dried French prunes from coastal regions


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

Authors Affiliations

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

Publication Information

Hilgardia 33(8):319-348. DOI:10.3733/hilg.v33n08p319. November 1962.

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Abstract does not appear. First page follows.


The prune industry of California, aware of increasing competition for the consumer food dollar, expects that any competitive gains will come primarily from improving the appearance and flavor of prunes. The quality of prunes may vary greatly under quite uniform conditions of processing and storage. Many of the factors responsible are found in the prunes themselves and are the consequence of microclimate, cultural practices, size of crop, maturity, and harvest procedure. The last two are subject to considerable control and were studied as part of a comprehensive research program during the 4-year period, 1950-1953. The four major varieties of prunes produced for drying in California were studied in their principal areas of production.

Additional studies were begun in 1956 to gain more information on coastal valley prunes. The results presented here show how multiple harvests influence the quality of the dried product.


Prunes are harvested by being shaken from the tree, but in California’s interior valley shaking is usually not selective for maturity and prunes of all maturities drop at about the same level of energy. This is because abscission layers are usually not formed. In cooler coastal climates, abscission layers do form, and shaking can be selective for maturity. Since ease of fruit removal by shaking is associated with temperature there can be considerable variation in the behavior of prunes in different orchards in anyone year, or in a single orchard in different years. This is particularly true of orchards in parts of Napa and Sonoma counties, where the climate may fluctuate from year to year between coastal and interior valley conditions.

Because of lack of abscission, all prunes in interior valley orchards are removed at one harvest. In coastal valleys, two to four harvests are customary.

Selection of Plots

Several weeks before the harvest season, plots were selected in seven coastal valley orchards (see table 1) considered representative of the prune orchards

Literature Cited

Association of Official Agricultural Chemists. Official and tentative methods of analysis. 1945. 6th Edition Wash., D.C.: AOAC.

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., Dempsey W. H., Esau Paul, Miller M. W. Physical and chemical changes in French prunes during maturation in coastal valleys. Hilgardia. 33(8):311-18. DOI: 10.3733/hilg.v33n08p319 [CrossRef]

Esau Paul. Procedures for conversion of color data from one system to another. Food Tech. 1958. 12:117

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

Maxie E. C., Claypool L. L. Heat injury in prunes. Proc. Amer. Soc. Hort Sci. 1957. 69:116-21.

Nichols P. F. Prune moisture content and processing. Fruit Products Journal. 1935. 14:211-13. 240-41, 332-34, 370-72

Claypool L, Miller M, Dempsey W, Esau P. 1962. The influence of harvesting procedures and storage on the quality of dried French prunes from coastal regions. Hilgardia 33(8):319-348. DOI:10.3733/hilg.v33n08p319
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