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 Alero 
and blood, should not be employed with eed apple and 
grape juices. Precipitation 1s 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 3 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 Saigon 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 
