VEGETABLE AND FRUIT DEHYDRATIOX 147 



toluene and continue distillation briefly, repeating as necessary to remove final 

 traces of water. Droplets of water adhering to the walls can be brushed down 

 with a tube brush or with a piece of rubber attached to a copper wire and sat- 

 urated with toluene. The whole operation should be completed within an hour 

 and after the receiving tube has cooled to room temperature the volume of water 

 collected is read. From this the percentage content of the sample can be 

 calculated. 



The apparatus must be kept clean with chromic acid cleaning solution and 

 factors of particle size, volume of toluene, and heating time must be held close to 

 the conditions used in calibration against the vacuum-oven method. 



ELECTRICAL METHODS 



With electrical methods an electrical property of the material is used 

 as an index of the moisture content. Instruments are on the market, 

 such as the Steinlite, Tag-Heppenstall, and the Moisture Register, 

 that have been designed for use with grains and other materials and 

 have recently been applied to dehydrated vegetables. These instru- 

 ments must be calibrated for specific commodities against the vacuum- 

 oven method. Moreover, because of a limited range they must be 

 factory-adjusted for the range of moisture levels (such as 1 to 16 per- 

 cent) over which they are to be used. For accurate work special cali- 

 brations are advisable for different varieties of the same commodity, 

 and also for the same commodity subjected to different processing 

 methods, such as time of blanching or temperature of dehydration. 

 While the manufacturers claim an accuracy of 0.2 percent, the readings 

 will probably show 7 greater deviations as a result of variations men- 

 tioned above and also variations in temperature of the sample. Com- 

 plete confidence can be placed in the measurements only when the 

 unknown sample represents the same material and is ground and 

 treated in the same manner as that used in preparing the calibration 

 curve. In spite of shortcomings these instruments can be of great 

 value in the plant by making it possible to follow the immediate 

 progress of drying in test runs or in regular plant operations, since 

 determinations can be made in about 5 minutes. 



Determination of Adequacy of Blanching 



Some changes that occur during blanching are solubilization of 

 starch, denaturation of proteins, plasinolysis of the tissue cells, and 

 destruction of enzymes. The relative importance of these changes in 

 assuring that the ultimate consumer will receive the best-quality prod- 

 uct is not known. However, it is now generally believed that most 

 vegetables (onions excepted) must be adequately blanched in order to 

 obtain a satisfactory product when subjected to present conditions of 

 commercial dehydration and storage. The changes that occur during 

 blanching depend on both the temperature that the commodity reaches 

 and the time it is maintained at that temperature. It is hardly fea- 

 sible for the processor to measure directly the internal temperature of 

 the vegetable as it passes through his blancher. Therefore, in order 

 to be sure that his blanching operation has been carried out properly, 

 the processor must rely on a test that will indicate the extent to which 

 the aforementioned changes have occurred. However, such a test can 

 be of real value only to the extent that the change which it measures 

 can be correlated with the stability and quality of the delrydrated 

 commodity. 



