Factors Affecting Temperature Reduction and Weight-Loss in Vacuum-Cooled Lettuce

Excerpt from the report Preface: More than 80,000 carloads of Iceberg-type lettuce are vacuum-cooled annually. Cooling by this method depends upon the evaporation of moisture from the leaves. To obtain adequate cooling, the lettuce must be subjected to vacuum conditions that will reduce the temperature quickly to 40° F or lower without causing freezing damage or wilting. This report discusses the various factors that affect the efficacy of cooling such as type of package, vacuum tank pressure, condenser temperature, rate of evacuation, free moisture on the lettuce and maturity of lettuce