71 







DRYING BY ARTIFICIAL HEAT. 



Though sun drying may be utilised to a great extent in many parts of 

 Australasia, yet artificial evaporation must necessarily be the method 

 adapted by the majority of fruitgrowers. This method can be practised 

 successfully in every district where fruit is grown, whereas sun drying 

 will only be serviceable in regions that are hot and dry. Various kinds" 

 of evaporators are in use, but though they differ considerably in detail 

 yet they all work on the same principle. This principle is to remove 

 the water contained in the fruits by means of swift moving currents of 

 strongly heated air. If the air current is not sufficiently hot and rapid 

 the fruit cannot be thoroughly well dried. The air may be sufficiently 

 heated, but if it does not pass through quickly the fruit will be more or 

 less cooked and deteriorated in quality. It is necessary to heat the air 

 to a much higher degree than would be required to bake the fruit in an 

 oven ; but the rapid circulation prevents injury from burning. Apples 

 will cook in boiling water at a temperature of 212 Fah., or bake in an 

 oven at 225 Fah. ; but they will not cook or burn in an evaporator 

 heated up to 300 Fah., provided the air current is strong. The 

 evaporation of the water is a cooling process, and as the particles of 

 vapour are driven from the minute cells the heat surrounding the fruit 

 is reduced. A heat of from 240 to 250 Fah. will be sufficient for the 

 purpose. As a matter of course, when the main portion of the vapour 

 has been evaporated the heat must be reduced, so as to prevent all risk 

 from burning. 



The necessary chemical changes are brought about in the most perfect 

 manner by the use of rapid currents of strong heat, In the firsc place 

 the albumen is coagulated precisely the same as in an egg when boiled, 

 whereas by slow drying with fire heat a considerable portion is lost. 

 There is also less loss in the soluble starch, which is an advantage. The 

 pectine, or fruit jelly, either remains in the cells or on the surface, 

 instead of decomposing to a considerable extent and passing off, as is the 

 case with slow drying. Then, again, the saccharine ferment contained 

 in all fruits is destroyed by the strong heat. If the natural starch, 

 albumen and glucose are not made indestructible by perfect drying, the 

 prepared fruit will absorb moisture from the air, be liable to get mouldy, 

 and finally turn sour and decay. Fruit prepared by evaporation, in the 

 proper way, may be kept for years if necessary, when tightly packed in 

 boxes or casks. On the other hand, if imperfectly prepared, it will 

 not keep long, and is quite useless for an export trade. 



The illustrations represent two distinct types of evaporators, of which 

 there are a number of kinds. The first of these is what may be termed 

 the upright class, to which the Zimmerman machine belongs. In these 

 machines the evaporating chamber is above the furnace, and the heated 

 air, after passing through the trays of fruit, escapes through a covered 

 chimney at the top. The second illustration represents a machine 

 known as Dr. Ryder's patent, and it is claimed for it that the air passes 

 off more quickly than in the upright evaporators, and that consequently 

 the fruit is more effectively dried. 



