10 Nov., 1917.] Evaporation of Apples. 677 



by coils are in course of constructinn in the Nortli-'West, but none of 

 them have been subjected to the test of practical use in competition with 

 other methods of drying for a sufficient length of time to enable one to 

 say vvhctlicr any of them will be commercially successful. 



The Tunnel Evaporator. 



The need of the prune-growing districts of the North-west for an 

 efficient and economical method of drying prunes led to the development, 

 in the early nineties, of a great variety of evaporating machines. In a 

 publication, entitled Prunes in Oregon, issued as Bulletin 45 of the 

 Oregon Agricultural Experiment Station in June, 1897, Professor U. 

 P. Hedrick, at that time horticulturist of the Oregon Station, described 

 seven types of prune evaporators, each known by the name of its manu- 

 facturer or patentee, then in use. Two years later, J. A. Balmer, 

 horticulturist of the "Washington Agricultural Experiment Station 

 {Prunes, Bulletin 38, "Washington Agricultural Experiment Station, 

 May, 1899), described four of these evaporators, with at least two others, 

 as being at that time rather generally used in Washington. Of all these 

 types of evaporators, only two have stood the test of years of practical 

 use, and it would probably be impossible to find one of the others in 

 operation at the present time. 



The ,prune tunnel, or tunnel evaporator, as used to-day in the North- 

 west has been gradually perfected by modification of the " Allen Eva- 

 porator," manufactured and patented by W. K. Allen, of Newberg, 

 Oregon, and described by both Hedrick and Balmer in the publications 

 just cited as in rather general use in Washington and Oregon. In so 

 far as one can judge from the rather unsatisfactory drawings and de- 

 scriptions given by these authors, the original Allen evaporator had most 

 of the essential desirable features of the modern tunnel, with the very 

 great disadvantage that the fruit, once placed in the tunnel, was out of 

 sight or control of the operator until drying had been completed. 



Tunnel evaporators have never come into general use in those parts 

 of the United States in which apples are the chief fruit to be evaporated, 

 since the labour involved in handling the fruit on trays makes the process 

 elightly more expensive than drying on kilns. "Wherever prunes and 

 berries make up a considerable part of the total volume of fruits to be 

 dried, tunnel evaporators may advantageously be used, since prunes must 

 of necessity be handled in trays, while loganberries and raspberries make 

 a very much better product when so treated. 



In its essential feature the tunnel evaporator consists of a long, 

 narrow room, with the floor and ceiling inclined uniformly from end to 

 end, and with a furnace below the floor. The room is cut into a series of 

 narrow chambers, the " tunnels," by parallel partitions, which may be 

 solid or merely an open framework of slats. In some of the larger and 

 more elaborate plants the trays upon which the fruit is spread are 

 loaded upon trucks fitted with an open framework to support and 

 separate them, and these trucks are rolled in one behind another at the 

 upper end of the tunnel until it is filled. The dry fruit is removed 

 at the lower end of the tunnel by withdrawing the truck carrying it, 

 when the others move down by force of gravity, permitting a new truck 

 to be rolled in at the upper end. This arrangement was a feature of the 

 Allen evaporator. It is objectionable in that the upper and lower trays 



