THE CLARIFICATION OF FRUIT JUICES. 5 



ent districts of France (hence presumably of different varieties) 

 show differences in the readiness with which coagulation of the pec- 

 tins is obtained, that neither green nor overripe fruits give satisfac- 

 tory results, that juices low in acid and tannin content coagulate 

 readily, and that successful coagulation is obtained only when fer- 

 mentation is prevented during the period of defecation. 



It has been impossible in the laboratory of the Bureau of Plant 

 Industry to produce such results as are described by these authors 

 without having recourse to some of the chemical treatments which 

 they suggest. At a temperature of 4° C. pectase is inactivated or 

 acts so slowly as to fail entirely to bring about coagulation of the 

 pectins. At higher temperatures alcoholic fermentation is not pre- 

 vented and usually proceeds so rapidly as soon to make it impossible 

 to classify the juice as unfermented. It is possible to produce almost 

 instantaneous coagulation of pectins by some of the chemical treat- 

 ments outlined by the French writers cited, but such treatments are 

 not to be recommended, for the reason that their employment seri- 

 ously detracts from the beverage quality of the juice. 



CLARIFICATION BY THE FORMATION OF A PRECIPITATE. 



Various methods of clarification employed in wine making and 

 vinegar making may be grouped together, since they all depend upon 

 the production in the liquid of a voluminous precipitate, which 

 gradually subsides, carrying down with it the particles causing 

 turbidity. A rather careful study of such methods indicates that 

 none of them can be expected to give satisfactory results with un- 

 fermented juices. The method of clarifying wines most widely em- 

 ployed by European wine makers and most fully discussed in works 

 on wine making is precipitation by the addition of tannin and 

 gelatin. Since the precipitate is the product of a definite chemical 

 reaction, perfect results are obtainable only when the quantities of the 

 reagents are exactly adjusted, a slight excess of gelatin forming a 

 stable colloidal suspension. But tannin is present in every fruit 

 juice (its quantity showing wide differences with varieties and con- 

 siderable differences in a single variety when grown in different 

 years or under differing cultural and environmental conditions), and 

 this tannin enters into the reaction with gelatin. For this reason the 

 amounts of tannin and gelatin to be employed must be determined 

 by experiment for every juice, and with such viscous materials as 

 grape and apple juices the outcome of such experiments can be cer- 

 tainly determined only after some days. This alone makes the 

 method impracticable. The further fact that the tannin of a juice 

 plays an essential role in determining its characteristic flavor and 

 that its removal results in marked alteration of flavor makes the 



