UNITED STATES DEPARTMENT OF AGRICULTURE 





IH BULLETIN No. 1025 bv 

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Contribution from the Bureau of Plant Industry 

 WM. A. TAYLOR, Chief 



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Washington, D. C. 



PROFESSIONAL PAPER 



January 23, 1922 



STUDIES IN THE CLARIFICATION OF UNFER- 

 MENTED FRUIT JUICES. 



By Joseph S. Caldwell, Plant Physiologist, Office of Horticultural and 

 Pomological Investigations. 



CONTENTS. 



Page. 

 Purpose and scope of the investiga- 

 tion 1 



Methods of clarification generally 



employed 3 



Clarification by means of 



enzyms 3 



Clarification by the formation 



of a precipitate 5 



Clarification by the use of inert 



adsorbing agents 6 



Page. 



Experiments with diatomaceous earth 



for clarifying fruit juices 12 



Purification of the earth 13 



Difficulties encountered in filter- 

 ing treated juices. 14 



Simple and effective methods of fil- 

 tration with diatomaceous earth_ 15 



Pasteurizing before filtering 20 



Filtration of freshly pressed juices_ 20 



Summary 26 



Literature cited 28 



PURPOSE AND SCOPE OF THE INVESTIGATION. 



When an unfermented fruit juice, such as that of apples or grapes, 

 is prepared and preserved by the methods ordinarily employed, a 

 more or less copious precipitate consisting of cellular debris and 

 heat-coagulable material is formed after pasteurization. This fact 

 is responsible for the usual practice of pasteurization and storage, 

 followed after an interval by transfer to the final containers and a 

 second pasteurization. Even when the formation of a coagulum in 

 the final container is thus prevented, the liquid remains permanently 

 turbid and opaque from the presence of considerable quantities of 

 suspended colloidal materials, which are unaffected by heating and 

 subsequent storage. In the case of a few heavily pigmented varieties 

 of grapes, such as the Ives, Concord, Clevener, and other purple 

 varieties, the intense coloration of the juices masks their turbidity 

 and renders them attractive to the eye. In most grape varieties, 

 however, the juices obtained are densely opaque, tawny yellow, or 



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