52 BULLETIN LU1. U. S. DEPARTMENT OE AGRICTJLTUKE. 



be constantly renewed, or two vessels of wash water should be pro- 

 vided, as suggested on page 34, as the fruit carries considerable 

 quantities of lye into the wash water. 



In addition to the dipping, the fruit, in some instances, is passed 

 OA*er a perforator, which in brief is an inclined plane provided with 

 very small pin points, in order to slightly puncture the skin of the 

 fruits as they pass over it. The pricking of the skin in this way 

 serves the same purpose as the checking of the skin mentioned above 

 in connection with the dipping. TVTiere the perforator is used it is 

 not necessary to carry the dipping quite as far as where it is not 

 used, though the lye solution should completely remove the bloom 

 from the fruit. T\ nile formerly much used, perforators are now 

 rather generally discarded, because the breaking off of needles in 

 the fruit was not an infrequent occurrence, and when lye dipping 

 is properly done, perforation is unnecessary. 



Combination machines are on the market which include equip- 

 ment for dipping, washing, perforating, and sizing the fruit, and 

 in which the fruit is automatically passed from one operation to the 

 next. TThere extensive operations are concerned, such an equipment 

 is essential, but smaller, more simple equipment involving all hand- 

 work serves the purpose very well for small-scale activities. 



The foregoing paragraphs describe the methods of checking the 

 fruit at present in use, It has been shown by investigators at the 

 Oregon Agricultural Experiment Station 8 that it is possible to dis- 

 pense entirely with the use of lye and to secure satisfactory check- 

 ing by the use of boiling water alone. It is necessary that the water 

 be actually boiling, hence the tank used should be large enough so 

 that the water will not be cooled below the boiling point by the vessel 

 of fruit. The treatment requires 20 to 60 seconds, the exact time 

 depending upon the ripeness of the fruit. By reason of its greater 

 simplicity and economy, and its equal effectiveness, hot-water dip- 

 ping should entirely replace the use of lye. 



After clipping, the fruit is spread on trays of the type already de- 

 scribed on page 26. A single layer of fruit only should be placed 

 on the tray, but care should be taken to fill it completely, as partially 

 filled trays interfere with proper distribution of the air currents. 

 It is then ready to be placed in the evaporator. 



HANDLING PRUNES IN THE EVAPORATOR. 



It is obvious from the foregoing that an evaporator of the kiln 

 type is not suitable for use in drying prunes. Any of the types in 

 which the fruit is placed in thin layers on trays or racks as de- 

 scribed above can be used. As a matter of fact, the tunnel type has 

 at the present time almost completely displaced stack, cabinet, and 

 various other types of driers which were formerly used for the dry- 

 ing of prunes. Figure 15 shows the exterior of a tunnel evaporator 

 in Oregon. The dipper and other equipment used in preparing the 

 fruit for drying is housed in the annex with a shed roof. 



Considerable must be left to the operator's judgment with regard 

 to the temperature at which the evaporator should be maintained. 

 If it is too high in the beginning there is danger of the fruit bursting 



8 Lewis. C. I.. Brown. F. R., and Barss, A. F. The evaporation of prunes. Oreg. Agr. 

 Exp. Sta. Bui. 145, 36 p., 28 fig. 1917. 



