- 3 - 



the initial temperature of lettuce has little effect upon its final temperature. 

 Experiments with spinach (?) showed the same results in this respect. The 

 initial temperature of celery, on the other hand, has a marked effect upon its 

 final temperature, a difference of about 10 degrees. This is probably due to 

 the smaller surface area-volume ratio of celery,, 



Many inquiries have been received regarding the possibility of vacuum-cooling 

 celery. This commodity is not readily vacuum-cooled (table 2). However, 

 possibly a double vacuum cycle, i 8 e., twc successive vacuum-coolings may be used 

 for celery (fig. I;). If a double vacuum cycle is employed, observations should 

 be made to see whether there is excessive shriveling. Other possible methods 

 would be to lengthen the time under vacuum (9), to wet the celery prior to 

 vacuum-cooling, or to use a greater vacuum (7)<» In the last method, however, 

 the possibility of freezing, especially of the leaves, would have to be 

 considered,, 



Relation of Type of Container to Rate of Precooling . Leafy vegetables 

 which were packaged in cellophane bags, packed in cartons, and stacked solidly 

 on pallets, were rapidly vacuum-cooled, whereas similarly handled commodities 

 were cooled very slowly by means of conventional cooling in cold air (9). 



In another experiment, lettuce was vacuum-cooled in fiberboard containers 

 and in unlined, wooden, wirebound crates at the same time to determine the 

 effect of type of container upon the rate of cooling. The results (fig. 5) give 

 further evidence that a commodity which can be vacuum-cooled rapidly can be 

 packed in any type of container without affecting significantly the rate of 

 cooling if there are some openings to permit the escape of air and water vapor. 



WEIGHT LOSS DURING VACUUM-COOLING 



It has been supposed by some that considerable water is lost by evaporation 

 during vacuum cooling. It has been calculated that to cool 100 pounds of 

 coleslaw from 70° F. to 35° it is necessary to extract approximately 2,325 B.t.u. 

 This would require the evaporation of about 2.2 pounds of water or about 2.2 

 percent of the weight. In actual practice, the weight loss of coleslaw during 

 vacuum-cooling was about 2.0 percent (9). The weight losses of several 

 commodities during vacuum-cooling are shown (table 5)o 



EFFECT OF VACUUM-COOLING ON QUALITY OF PRODUCE 



Weight losses during vacuum-cooling are small, and shriveling or wilting 

 in vegetables has not been a problem in commercial vacuum-cooling. 



Brown spot of lettuce which is troublesome at times has been attributed to 

 suffocation during vacuum-cooling (11). However, brown spot also occurs in 

 lettuce which has not been vacuum-cooled. Further, some lettuce has been 



