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



method useless for fruit juices. The same objections apply to the 

 use of such materials as fish glue, egg albumen, milk, casein, and 

 blood ; the precipitation obtained with these substances is due to re- 

 action with tannin or the acids present, or both, with consequent 

 alteration of flavor. 



As the work of La Marca (16) upon the effects of clarifying agents 

 on the chemical composition of wines has shown, perceptible altera- 

 tion in flavor as well as in chemical composition of the wine results 

 from the employment of such materials, which led La Marca to 

 advise strongly against their use by wine makers. 



A rather careful study carried on in the laboratory of the Bureau 

 of Plant Industry has yielded results showing conclusively that the 

 use of any of the nitrogenous materials previously mentioned as a 

 clarifying agent for unfermented fruit juices is highly inadvisable. 

 The viscosity of most juices is sufficiently high to make the subsi- 

 dence of the precipitate extremely slow and incomplete. All the sub- 

 stances used are complex protein mixtures containing constituents 

 which are to some degree soluble in the juice, and the introduction of 

 such sources of nitrogen makes the liquid a better medium for the 

 growth of molds. The alteration of flavor produced by the loss of 

 tannin and the introduction of foreign material is perceptible in all 

 juices and amounts to denaturation in the case of the more delicately 

 flavored ones. For these reasons the use of such methods with un- 

 fermented juices is ineffective and injurious. 



CLARIFICATION BY THE USE OF INERT ADSORBING AGENTS. 



The third group of methods for clarifying colloidal solutions or 

 suspensions is that employing chemically inert solids as adsorbing 

 agents. Methods of clarifying wine and vinegar and some other 

 liquids by means of such materials as fuller's earth and Spanish clay 

 have , been developed empirically and have been in use for long 

 periods, while the use of carbons in decolorizing cane juice has been 

 discussed in the literature, according to Zerban (3J{) ■> since 1785 ; but 

 it is only very recently that much attention has been devoted to the 

 study of solid adsorbents for clarifying fruit juices. 



CARBONS AS CLARIFYING AGENTS FOR FRXTIT JCICES. 



The studies of solid adsorbents made in the laboratory of the Bu- 

 reau of Plant Industry began in 1918 with a study of a considerable 

 number of carbons, which included, with others, samples of a number 

 of special filtering carbons supplied by American manufacturers and 

 various samples of purified animal charcoals obtained through chemi- 

 cal supply houses. The work included the treatment of a large num- 

 ber of apple and grape juices, immediately after pressing or after 



