306 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



In different sections the specific gravity of the good fruit may be 

 higher or lower than that found in the experiments here recorded, but 

 the general conclusion will be the same in the various districts, namely, 

 that the specific gravity of good fruit will increase in storage and that 

 of frozen fruit will decrease. 



The explanation of the change in specific gravity of sound and 

 frozen fruit seems to be as follows: Freezing kills the walls of the 

 cells in the fruit and so changes it from a living, semi-permeable 

 membrane to a dead, porous mass, acting like a sponge. In the frozen 

 fruit, therefore, connection is established between the rind and the 

 pulp and the water which is evaporated from the outside of the rind 

 is supplied from the pulp without the fruit suffering much diminution 

 of volume. Losing weight and retaining approximately its original 

 volume, it must, obviously, decrease in specific gravity. The unfrozen 

 fruit on the other hand, loses very little, if any, moisture, except from 

 the rind. This shrinks down very markedly and so decreases the 

 volume of the fruit. As the weight does not decrease proportionately, 

 the specific gravity increases. The difference in the evaporation from 

 the rind is shown very clearly in figure 18. These two oranges were 

 picked on January 13 and stored for two months. They were the 

 same size, 3% e inches in diameter, on picking. When they were cut 

 the sound fruit had decreased to 2% inches while the frozen one had 

 lost only % 6 inch, measuring 3 inches in diameter. 



SPECIFIC GKAVITY OF JUICE 



It was not possible to make a determination of the specific gravity 

 of the juice on all of the samples used on account of their large num- 

 ber; therefore, the data which is presented in table 3 shows a rather 

 irregular appearance. The specific gravity of the juice of unfrozen 

 oranges in storage does not seem to change appreciably but it remains 

 consistently greater than that of the frozen oranges. The juice of the 

 frozen oranges in storage had an average specific gravity of 1.046 

 throughout a greater part of the experiment and increased quite 

 markedly toward its expiration. The juice of the sound oranges had 

 an average of 1.052 which remained approximately constant. The 

 specific gravity of the juice of frozen oranges picked at different 

 intervals did not increase, as with frozen oranges in storage, but 

 remained constant (see table 7). 



The average specific gravity of the juice of the lemons showed 

 about the same differences. The juice of the sound fruit had a higher 

 specific gravity than that of the frozen. There are more irregularities 



