24 BULLETIN 1025, IT. S. DEPARTMENT OF AGRICULTURE. 



Rommel, Wilder, and Woodruff show material alteration in flavor 

 after heating to 175° F. and filtering. There is also perceptible 

 alteration in the flavor of apple juice, irrespective of variety, when 

 so treated. The alteration in flavor is apparently identical with that 

 which occurs when such juices are heated to pasteurizing tempera- 

 tures in open vessels and is undoubtedly due to the loss of volatile 

 constituents from the hot liquid during the unavoidable exposure to 

 the air which occurs during filtering. 



Experiments designed to determine the degree to which the heat- 

 ing of apple juices and the more easily injured grape juices may be 

 carried without noticeable loss of characteristic flavor and quality in- 

 dicate that the danger line for such juices lies between 130° and 140° 

 F., when the liquid is slowly raised to this temperature in a tank 

 heated by a steam coil or by placing it in open vessels sunk nearly to 

 the top in a water bath. Juices heated to 130° F. in this manner, 

 mixed with earth, and filtered hot showed no alteration in flavor. 

 When heated to 140° F. and filtered while hot, such apple juices as 

 those of York Imperial, Northern Spy, and Grimes, and such grape 

 juices as those of Delaware, Isabella, Missouri Riesling, and Rommel 

 were not perceptibly changed in flavor, while with such apple juices 

 as those of Delicious and Winesap and such grape juices as Catawba, 

 Goethe, Salem, Brilliant, and Brighton there was a distinct diminu- 

 tion in flavor. In the case of all these juices there was quite marked 

 alteration in flavor in the lots heated to 150° F. before filtering, and 

 the effect became more pronounced with the increase of the time dur- 

 ing which the samples were kept at this temperature. 



For these reasons, heating as an aid to filtration can be recom- 

 mended only in cases in which the temperature can be rather closely 

 controlled, and in no case should it be allowed to rise above 130° to 

 140° F. or to remain at this temperature more than a minute or two. 

 Heating to these temperatures is insufficient to cause precipitation of 

 the heat-coagulable material present in the juice, but very consider- 

 ably increases the rate of filtration by diminishing the viscosity of 

 the juice. 



EXPERIMENTS WITH GRAPEFRUIT JUICES. 



In the work with grapefruit juices reported by Chace (<5), the 

 juices were pressed, pasteurized, stored for some weeks until sedi- 

 mentation had become fairly complete, decanted, mixed with diato- 

 maceous earth, filtered, bottled, and pasteurized. It occurred to the 

 writer that it might be possible to eliminate the preliminary pasteuri- 

 zation and subsequent period of storage in the case of grapefruit 

 juice by applying to the freshly pressed juice the same methods found 

 effective with apple and grape juices. This it has been possible to do. 



