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



distinctive flavor." The results obtained by the Bureau of Plant Industry with 

 a large number of apple and grape juices indicate that carbon has too much 

 effect upon flavor to permit its use with apple juices or with any but the more 

 strongly flavored grape juices. 



(4) The various carbons differ materially in the degree of transparency 

 which it is possible to produce in a given juice by their use. In part, these 

 differences are due. to differences in adsorbing surface presented by equal 

 weights of material ground to unequal degrees of fineness, but in part they are 

 specific differences due to differences in porosity, in ash content, or to other 

 factors not controllable by separation of the samples into particles of like 

 size by screening. The results indicate that the character and amount of ash 

 in a given carbon may have considerable significance in determining the 

 efficiency of the carbon in the removal of colloidal material of the nature here 

 dealt with, namely, pectins and gums. A certain sample of animal charcoal, 

 when prepared for use in the usual manner by treatment with hydrochloric acid 

 and washing free of acid with water (20, p. 22; 31, p. 88), gave a clearer, 

 more brilliant product than any other carbon. When this charcoal was sub- 

 jected to exhaustive treatment in order to remove salts as completely as pos- 

 sible, its clarifying efficiency was reduced practically to the level of other 

 carbons. This, of course, suggested that it may be possible to improve the 

 efficiency of carbons for the particular purpose here aimed at by preliminary 

 chemical treatment, but the fact that carbons are not well adapted to the 

 purpose in other respects made it appear inadvisable to follow up the suggestion, 

 especially since Zerban and his associates (34, 36, 37) already have under 

 investigation the broader problem of the particular property or constituent of 

 carbons which gives them clarifying power. 



(5) The removal of pectins and gums by carbon is very incomplete in the 

 case of apple and grape juices, as Zerban (34) has shown to be the case in 

 cane juices. Consequently, the pasteurization of juices clarified with carbon 

 is followed by the formation of a considerable precipitate unless such juices 

 have been subjected to preliminary pasteurization followed by the removal 

 of the heat-coagulable material prior to treatment with carbon. This double 

 pasteurization is to be avoided if possible, as it materially increases the labor 

 and cost of handling, while at the same time increasing the loss of flavor. 



(6) Considerable difficulty is encountered in dealing with viscous juices 

 after the addition of carbon, even when subjected to preliminary pasteuriza- 

 tion, as a result of the fact that a portion of the added carbon forms a per- 

 sistent suspension in the liquid. This can not be removed by any of the usual 

 methods of filtration, and when juices so treated are pasteurized and stored 

 there is a slow deposition of carbon upon the sides and bottom of the con- 

 tainers. Gore (14) encountered this difficulty and found it necessary to add 

 diatomaceous ( " infusorial " ) earth and to filter in order to remove the carbon. 

 His process as applied to the more difficult juices consequently involved a pre- 

 liminary treatment with infusorial earth and filtration, treatment with carbon, 

 a second treatment with earth, and a second filtration. As some time must be 

 allowed to permit sedimentation after each step in the treatment, the process 

 is laborious and requires rather careful temperature control to prevent fer- 

 mentation. The repeated handling necessarily involves a greater danger of 

 infection with mold spores and increases the difficulty of securing perfect pas- 

 teurization. 



In view of the many serious difficulties encountered in the use of 

 carbon and the decided denaturing effects upon color and flavor of 

 all but the most strongly flavored and deeply colored juices, it 



