26 BULLETIN 1025, U. S. DEPARTMENT OF AGRICULTURE. 



of clarification and bottling with grapefruit juice by the employment 

 of the same general methods found successful for apple and grape 

 juices. 



SUMMARY. 



(1) The usual methods of filtration do not give satisfactory re- 

 sults when applied to unfermented apple, grape, and grapefruit 

 juices, as such juices are difficult to filter and contain considerable 

 quantities of colloidal material which pass through ordinary filters. 



(2) Various methods of treatment designed to assist the clarifica- 

 tion of these juices have been studied with a view to developing a 

 means of making clear, transparent juices which would be applicable 

 on a small scale. 



(3) Clarification by means of enzyms can be accomplished, but 

 the technical skill and the degree of control of conditions required 

 in the work are such that the method is not adapted to general use 

 in small-scale juice manufacture. 



(4) The methods of clarification employed by wine makers, such 

 as the addition of tannin and gelatin, casein, fish glue, egg albumen, 

 and blood, should not be employed with unfermented apple and 

 grape juices. Precipitation is slow and incomplete, the chemical 

 composition of the juices is altered, and the palatability and flavor 

 are decreased. 



(5) Of the inert adsorbing agents used as aids in clarification, 

 carbon is not suited for use with apple and grape juices. Carbons 

 remove flavoring substances and have high decolorizing power and 

 do not wholly remove pectins and gums. Carbon also forms persist- 

 ent suspensions which pass through ordinary filters and ultimately 

 deposit upon the sides of the container. 



(6) The preparation of a suitable silicic-acid gel is tedious and 

 difficult, the precipitation of colloidal material obtained by its use 

 is imperfect and slow, and the filtration of juices so treated is diffi- 

 cult because of the prompt clogging of filters. 



(7) Diatomaceous earth is by far the most satisfactory aid to the 

 filtration of fruit juices yet employed. It is highly efficient in the 

 removal of colloidal materials and does not remove coloring and 

 flavoring substances. 



(8) As obtained in the markets, diatomaceous earth contains vary- 

 ing amounts of wax derivatives which impart perceptible foreign 

 flavors to most juices. These objectionable materials are readily re- 

 moved by heating the earth to redness for a short time. Earth which 

 has been used may be repeatedly " revivified " for further use by a 

 similar treatment. 



(9) Juices which are to be clarified by the use of diatomaceous 

 earth should be allowed to stand undisturbed for 12 to 18 hours 



