VEGETABLE AND FRUIT DEHYDRATION 13 



at this point tends to prevent excessive humidity in the preparation 

 room by condensing steam escaping from the front end of the 

 blancher. Elimination of all unnecessary handling of the material 

 reduces the amount of labor and equipment needed and results in 

 a better finished product. 



To be effective, the preparation line must be carefully laid out, with 

 sprays at intervals to keep the product moist, and with no pockets that 

 permit accumulation of vegetables which later contaminate the entire 

 lot with discolored, oxidized products. Washers, either spray or rotary 

 types, placed at intervals in the line tend to keep the product wet and 

 clean. This is good sanitary practice. 



Arrangement of floor drains beneath the preparation lines to carry 

 off the water is necessary. This prevents accumulation of waste water 

 and residues from the line which would soon become sour and create 

 odors in the plant. 



The best preparation line is one that continuously gets the product 

 to the drier in the shortest time allowed by proper operating pro- 

 cedures. These procedures vary slightly from plant to plant and 

 considerably with one vegetable or another. 



Dehydrator 



Choice of drier. — Three types of vegetable dehydrators are shown 

 in figures 1 to 5. Figure 1 shows a plant capable of handling 100 

 tons of raw product per day, in continuous operation. The dehy- 

 drator is of the multistage tunnel type. Figures 2 and 3 show 50- 

 and 25-ton plants with dehydrators of the counterflow tunnel type ; and 

 figure 4, a 25-ton plant with a conveyor-type drier. All are planned 

 to include finishing bins. 



This presentation is not meant to imply that a multistage unit is 

 better for a 100-ton plant, and a conveyor type for a 25-ton plant. The 

 examples are presented for illustrative purposes only and it is possi- 

 ble that each of these types will prove to be suitable in a wide range 

 of plant capacities. The capacities indicated are only nominal; the 

 true capacity of each is dependent upon the product, the drier design, 

 heat input and air circulation, and the use of finishing bins. 



In the multistage drier, the material passes first through a parallel- 

 flow tunnel, then through a counterflow tunnel, and finally into fin- 

 ishing bins. If properly designed, this is a very flexible type of unit, 

 permitting the adjustment of drying conditions to the optimum for 

 product quality. The second-stage tunnels, used alone, are suitable 

 for fruit drying. 



The counterflow tunnels illustrated in the 50- and 25-ton plants 

 are a conventional type. Drying times are not as short as in multi- 

 stage units because the maximum temperature of the air is limited 

 by the highest temperature that the product at the dry end can stand. 

 The use of finishing bins, permitting removal of the product from 

 the tunnels at a higher moisture content, partially offsets this draw- 

 back. 



The conveyor type of drier shown in the 25 -ton plant has shown 

 promise in commercial operation and will doubtless be used increas- 

 ingly as its operating problems are overcome. 



Figure 5 shows the lay-out for a plant handling 400 pounds of 

 potatoes per hour. If the operation is continuous, the plant will 



