VEGETABLE AND FRUIT DEHYDRATION 23 



Batch-type drum washers are generally suitable only for use in the 

 very smallest dehydration plants, or in connection with institutional 

 or community dehydrators. 



The brush washer is quite commonly used, but it is limited because 

 of mechanical complications due to brush failure. The product in 

 the washer is caused to pass over or along between rotary brushes. 

 These brushes are usually made from water-resistant, tough fiber 

 bristles or, in some cases, of rubber fingers. The adjacent brushes 

 usually run in alternate directions or at different speeds in such a way 

 that the product is rotated and brushed simultaneously as it pro- 

 gresses. The retention time is governed by the flight path or by the 

 rate of charging, which has the effect of crowding the washed product 

 out of the washer. The units are best suited to removing sandy loam 

 but may be used to remove heavier soils. 



Shuffle or shaker washers, although very efficient, are mechanically 

 complicated. Their vigorous reciprocating action produces violent 

 scrubbing and tumbling of the product, and hence even the most stub- 

 born mud can be removed. When equipment of this type is used the 

 supporting structure must be firm in order to prevent objectionable 

 vibration. 



In any type of mechanical washer the rubbing and abrasive action 

 can be powerfully reinforced and supplemented by proper distribu- 

 tion and control of the supply of wash water. The water may have 

 two distinct functions. When it is supplied in the form of vigorous 

 sprays it has a very effective scouring action which will cut away tight- 

 ly adhering patches of clay and dislodge dirt from the bottom of 

 wrinkles and eyes that are out of reach of surface rubbing or brush- 

 ing. In addition, the flow of water down over the material flushes 

 away the loosened dirt and removes it from the washer. Both of 

 these actions are desired. The first calls for sufficient water pressure 

 and careful placing of the sprays. The second calls for a sufficient 

 volume of water. In a rotary-drum washer the stream of vegetables 

 is carried by the rotation of the drum well up on the ascending side of 

 the drum, whence they are constantly rolling downhill toward the 

 bottom. The water sprays should be carefully directed to cover thor- 

 oughly this sector on the ascending side of the drum. 



Drain lines beneath vegetable washers should be provided with 

 easily accessible dirt traps, since much of the dirt and sand carried 

 by the wash water will be so heavy as to settle immediately in an or- 

 dinary sewer line and plug it. 



The amount of washing required will vary throughout the season, 

 and therefore ample facilities should be provided to care for the prod- 

 uct under the most adverse conditions. The installation should also 

 be sufficiently flexible to permit rearrangement of the equipment 

 whenever necessary. 



Loose leafy vegetables. — Cut vegetables, such as spinach, chard, 

 parsley, etc., are usually washed in drum washers fitted with water 

 sprays, or in tanks. The former means offers a continuous process and 

 is, therefore, most commonly used. Shuffle and brush washers are 

 obviously unsuitable. 



Retention time in a drum washer will vary with the condition of the 

 product, and the character and quantity of soil to be removed. Spray 

 nozzles that provide a good scouring action without tearing, ripping, 

 or otherwise injuring the product should be chosen. 



