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



10 per cent more time to pass through the filter, as a result of a 

 greater tendency to clog the disk with slime, but gave a slightly 

 greater yield of filtered juice than the others, since it was possible 

 to reduce the sludge to a drier condition. The juices which had re- 

 ceived the preliminary treatment filtered more quickly and with less 

 clogging, but the bulky sludges could not be satisfactorily filtered dry. 



In other experiments juices treated with earth were held for 

 longer periods at lower temperatures, in order to prevent fermenta- 

 tion while allowing sedimentation to become complete. Here one 

 encounters a difficulty arising out of the fact that as the temperature 

 at which the juice is held is lowered, the viscosity of the liquid is in- 

 creased, slowing down the rate of sedimentation and making it less 

 complete. 



A rather extended series of experiments has shown conclusively 

 that the additional handling necessary and the greater loss of juice 

 resulting from inability to filter the sludges satisfactorily make a 

 preliminary treatment with earth followed by sedimentation before 

 filtering inadvisable. A larger yield of filtered juice is obtained 

 with a smaller expenditure of labor when the juice is allowed to 

 stand undisturbed for 12 to 24 hours after pressing in order to allow 

 the settling out of cellular debris, then decanted, mixed thoroughly 

 with earth, and immediately filtered. 



SEDIMENTATION BEFORE FILTERING. 



A period of sedimentation before filtering is quite necessary and 

 should never be omitted if an effort to obtain a perfectly permanent, 

 clear, brilliant filtrate is being made. When either apple or grape 

 juice is taken directly from the press, mixed with earth, and filtered, 

 the liquid coming through the filter is perfectly transparent. On 

 bottling and pasteurizing such juices and allowing them to stand 

 for some time, however, cloudiness or haziness appears. The degree 

 of the change varies greatly with various fruits, but all juices so 

 treated become in some degree turbid colloidal solutions, while in 

 some cases a deposit is ultimately formed in the bottles. Check 

 samples of the same juices allowed to stand for 12 to 24 hours before 

 treatment do not show this behavior, but remain permanently free 

 from cloudiness or sediment. 



The explanation of the facts just stated is not known, and only 

 unproved hypotheses can be suggested. When the cells of the fruit 

 are ruptured and the juice expressed and exposed to the air various 

 constituents are brought together which were previously separated 

 from one another in the cells but which are capable of reacting when 

 brought into contact. The intercellular materials (pectin and its de- 

 rivatives) are brought into contact with the acids of the juices and with 

 pectase. It is conceivable that under such conditions a conversion of 



