Methods of Drying 79 



The temperature of the stack should run from 160 

 to 180 Fahrenheit. One important essential is a strong 

 draft of fresh air through the machine. A large amount 

 of vapor is given off by a machine full of hot, green fruit, 

 and it needs to be removed and replaced with dry air as 

 rapidly as possible. Much more fruit can be dried in a 

 bright, fair day, with a brisk northwest wind, than in a 

 damp, cloudy and still day. In some of the large hori- 

 zontal machines the necessary draft of air is secured from 

 large fans revolved by steam power. 



The commonest type is some form of stack in which 

 the trays are put in at the bottom, directly over the heat, 

 and gradually lifted to the top as others are put in be- 

 neath. When dry they are taken out on the floor above, 

 the trays being returned to the lower floor for refilling. 

 One serious objection to this method is the fact that the 

 work must be timed and a tray put in just often enough 

 so that a dry one can be removed from the top. This is 

 not easy, even with experience, for as above noted, weather 

 conditions greatly modify results. A type described by 

 Corbett 1 reverses this operation, putting in the green 

 fruit at the top and removing the dried product at the 

 bottom. The advantage claimed for the method is that 

 the vapor from the green fruit will be more quickly re- 

 moved without passing over that which is more nearly 

 dry, and that quicker results, less dependent on atmos- 

 pheric conditions, are to be obtained. A modern type 

 evaporator is shown in Plate III. 



In the Williams evaporator, one of the earlier makes, 

 the trays were placed on hangers attached to endless 

 1 Farmers' Bulletin, No. 213, U. S. Dept. of Agr. 



