10 Xov., 1017. 1 Evaporalion nf Apples. 683 



of zinc. While this amount is much less than is found in fruits dried on 

 well-galvanized trays, it may be readied or exceeded when an inferior 

 wire is used in making trays, or when trays become rusty from long 

 continued use. The employment of wooden trays offers a theoretical 

 solution of the difilculty, but unfortuii:itely there are practical difficulties 

 which prevent their use; such trays aic expensive to make and heavy to 

 handle, the strips making up the bottom must be so narrow, in order not 

 to impede the circulation of air, that they are very fragile, unless made 

 of some hard, tough wood, as hickory or rattan, and the fruit sticks 

 rather badly unless the trays are oiled. For all these reasons, the use of 

 metal trays seems practically unavoidable, but the operator should 

 promptly discard those in which the destruction of the zinc coating has 

 occurred.* To paint such trays with white lead, as some operators do, 

 is simply to add the more poisonous metal lead to the fruit, and such 

 treatment of trays is fraught with danger of serious consequences to 

 the consumer of the product. 



The Operation of the Tunnel Evapobatoh. 



The method of operation of the tunnel evaporator differs from that of 

 other driers in two respects : first, the fruit is subjected at the beginning 

 of the pi-ocess to a very moderate temperature, which is steadily increased 

 as the drying proceeds ; second, the warm air at its first entrance to the 

 tunnel comes into contact with the dryest fruit, then with that containing 

 more and more water, until it reaches fresh fruit, and becomes saturated 

 with moisture immediately before finally passing out of the tunnel. It 

 is generally claimed that such fruits as apples and berries retain more 

 of their natural flavour when subjected to a temperature not higher than 

 120-135 degrees Fahrenheit in the first hours of drying, but that the tem- 

 perature may advantageously be gradually raised to 150-165 degrees 

 after the fruit has given up a portion of its water content. There is the 

 additional advantage that berries kept at 120-135 degrees until drying 

 is well begun do not have their cellular structure broken down, hence do 

 not run together into compact masses, while neither berries, prunes, nor 

 apples lose a portion of their sugar by " bleeding " or dripping, as is 

 the case when materially higher temperatures are used at the outset. 

 Consequentlj' a heavier product with a larger sugar content is obtained 

 by maintaining a moderate temperature at the outset, facilitating the 

 drying by increasing the heat only after the fruit has lost so much water 

 that dripping no longer occurs. The tunnel evaporator provides at one 

 time the various temperatures needed, since it is hottest at the lower end, 

 directly over the furnace, and the temperature steadily decreases toward 

 the upper end; also the temperature at any point near the top of the 

 tunnel is considerably below that at a corresponding point near the 

 bottom. Consequently, fresh fniit introduced at the upper end of the 

 tunnel, near the top, and pushed along the tracks until it is finally 

 removed dry at the lower end, is subjected to a steadily increasing tem- 

 perature throughout its stay in the tunnel. 



The second distinctive feature of the tunnel evaporator has an obvious 

 advantage. The heated air upon entering the tunnel passes over fruit 



• TIk- toUuwin^ noil- i^ suitpliid t.y M . .T. r.irirll. Oiclitid Siipt-rvisor. Victorian Ut'Partmi-nt of 

 Agriculture :^It" the wire netting of the trays be painted with laequer and thoroughly dried before the 

 trays are used, the spelter will be protected from the corrosive action of the apple acids in combination, 

 or wliea mixed with the residue of the salt solution and that of the sulphur fumes. 



