vacuum-cooled for 8 hours and then stored for 3 weeks at 38° F. without any 

 evidence of suffocation or brown spot e 2/ 



Apples, potatoes, and tomatoes have suffered some injury during vacuum 

 cooling (6, 8) 9 but no serious consideration has been given to cooling them by 

 this process. Aside from these commodities, no impairment of either flavor or 

 quality has been observed in ether vacuum-cooled fruits and vegetables. 



Trade publications have stated that the vacuum process destroys bacteria 

 which cause decay in lettuce „ No evidence has been seen to substantiate this 

 statement o The resistance of bacterial ceils to adverse conditions is well 

 known and it is probable that if the vacuum were to rupture bacteria, it would 

 also injure the vegetable cells* In fact, a common method of preserving 

 bacteria is to freeze-dry them under extremely high vacuum. 



Inhibition of decay by vacuum-cooling is probably a result of thorough 

 precooling plus drying the surfaces of produce. Low temperature is the 

 principal inhibitor of decay In a comparison of dry-packed, vacuum-cooled 

 lettuce and ice-packed, non-vacuum-cooled lettuce, little difference was found 

 in the amount of waste under strictly controlled conditions (12.). 



SOME ECONOMIC CONSIDERATIONS OF VACUUM-COOLING 



According to trade reports the initial investment- for vacuum equipment is 

 high, and apparently operation over long seasons is necessary to justify the 

 costs involvedo The latest development has been the construction of vacuum 

 chambers large enough to accommodate a loaded refrigerator railroad car or 

 truck trailer (13) 



Vacuum-cooling has created a revolutionary change In the handling of 

 lettuce The process permits the use of any tj^pe of container for packaging o 

 Lettuce can be packed in the field, eliminating the need for a packing house . 

 It is no longer necessary to use packaged ice or to top-ice the lettuce in 

 transit, and space is thus better utilized,, Burkhart (2) has estimated that 

 lettuce packing and shipping costs have been reduced 25 percent since the advent 

 of vacuum-cooling » 



It can be anticipated that if new large acreages are planted to lettuce, 

 vacuum=cooling plants will be constructed. Also, there will probably be further 

 refinements in vacuum-cooling of lettuce and its use extended to prepackaged 

 lettuce o 



Spinach, coleslaw, and mixed sa?.ad can be hydrocooled (flooded or immersed 

 in ice water) prior to packaging, but by the time they are spun-dried and 



2/ Unpublished data by G. L. Rygg and D„ H c Dewey o 



