Circular No. 619 



September 1941 • Slightly Revised February 1942 



Washington, D. C. 

 UNITED STATES DEPARTMENT OF AGRICULTURE 



Preservation of Fruits and Vegetables 

 By Commercial Dehydration l 



By E. M. Chace, principal chemist, W. A. Noel ; associate industrial engineer, 

 and V. A. Pease, 2 associate microscopist, Bureau of Agricultural Chemistry and 

 Engineering 



CONTENTS 



Introduction 1 



Preservation by dehydration 1 



Dehydration industry 2 



Dehydration plant 3 



Selection of material 4 



Preparation of material 4 



Washing 4 



Grading for size 4 



Peeling 5 



Trimming--- 5 



Checking 5 



Subdividing 5 



Pitting and seeding 6 



Traying fi 



Conveying the trayed material -. fi 



Pretreatment 6 



Blanching or processing 7 



Sulfuring 7 



Drying 7 



Types of driers 7 



Page 

 Dr y ing — C ont inued 



Heat 10 



Air li 



Moisture in the air 12 



Relation of drying conditions to drying 



rate and quality of product 12 



Engineering calculations for designing a 



tunnel drier 18 



Drying by recirculation of air 23 



End point of dehydration 27 



Curing 27 



Insects attacking dried fruits 28 



Packing and storing 28 



Detailed directions for drying 29 



Fruits 32 



Vegetables 34 



United States patents 37 



Literature cited 41 



Supplementary bibliography 42 



+** * +** * ** * 



INTRODUCTION 



The investigation here reported was undertaken to determine 

 certain physical principles and their application to dehydration 

 problems in general. The project was not carried to the point where 

 it was possible to consider the modifications necessary for the different 

 varieties of fruits and vegetables. Factors leading to the deteriora- 

 tion of dehydrated products and the relation which the condition of 

 the fresh material may bear to this deterioration are important 

 phases of the problem not here considered. 



PRESERVATION BY DEHYDRATION 



Spoilage of raw food is due principally to the growth of molds and 

 bacteria. This growth does not occur w r hen the soluble solids are 

 sufficiently concentrated through the reduction, by drying or by other 

 means, of the water present in foods. Even if they are not killed, 

 the molds and bacteria remain dormant and harmless in the absence 



1 Supersedes Department Bulletin 1335, Commercial Dehydration of Fruits and Vegetables. 

 "■ Died April 30, 1941. 



440721°-42 1 



