22 MISC. PUBLICATION 5 4 0, U. S. DEPT. OF AGRICULTURE 



PREPARATION OF RAW MATERIALS 



Washing 



Root vegetables. — Root crops received from the field are sometimes 

 laden with mud and debris, and must be thoroughly cleaned before 

 they are peeled, since dirt or sand on the vegetable will interfere with 

 any kind of peeling operation. The difficulty of cleaning depends 

 on such factors as type, variety, age, and condition of the product, 

 as well as type and condition of the soil. In localities where produce 

 has previously been prepared for the fresh market, adequate cleaning 

 procedures have probably already been established. In such cases, 

 it is suggested that a study be made of the adaptability of these 

 methods to a new processing line. 



Root crops are usually cleaned in two or more steps. A dry shaker 

 screen will remove much loose dirt and trash. Loose dirt is then 

 washed away in a water spray or bath. The equipment required for 

 this preliminary Avash is generally incorporated into a unit which 

 performs a dual function. For spray washing the sprays are located 

 on the elevator, which also serves as a conveyor to the main washer ; 

 for washing in a bath the product is allowed to soak in the boot of 

 the same elevator. The latter method is preferred, as it tends to even 

 out the surges caused by intermittent loading (fig. 9). 



Figure 9.- 



-Elevators : A, Equipped with water sprays ; B, equipped with boot 

 washer. 



The final washing operation can be carried out in any of several 

 commonly used types of washers, such as the rotary drum, the brush, 

 and the shaker washer. Most of these units are equipped with water 

 sprays, the intensity of which may range from normal city water 

 pressure to several hundred pounds per square inch. High-pressure 

 water sprays ordinarily require the use of booster pumps. 



Because of its simplicity, the rotary-drum washer is the one most 

 widely used. The severity of its action can be varied by changing the 

 roughness of the drum surface. If longitudinal slots are used, open 

 spaces between the slots will facilitate the ejection of sticks, rubble, and 

 peewee-sized products. The retention time will determ ine the degree 

 of washing for any given washer. Control of this factor in a con- 

 tinuous washer can be accomplished by varying the degree of tilt of 

 the drum, varying the drum speed, or more positively by providing 

 an internal helical guide fence to regulate the advance of the product. 



