One problem with many tropical fruits is disposing of the heavy crops in relatively short bearing seasons with minimum wastage (how many Bowen mangoes rotted on the ground last December?) For many years, canning and bottling have been the most popular methods, but both present problems in outlay of capital and storage space.

One of the oldest ways of preserving food is drying, and with the revival of natural methods, drying is presently undergoing a worldwide revival, it being both low in cost and efficient in use of energy.

Properly dried food is nutritionally superior to canned or bottled food, flavour and colour are maintained, only one-sixth of the storage space is required. Dried food is instant food and can be eaten without further preparation. Drying requires a fairly constant temperature of between 95 and 140°F, the majority of fruits drying best around 110°. A considerable proportion of the world's dried fruit, apricots, apples etc. are naturally sun-dried. This method is ideal in many parts of Australia; all that is required being to spread the fruit evenly on trays covered with net to keep off insects. Sun-drying has several advantages: costs are low, the only investment simply being drying trays and protective netting. There is almost no limit on the quantity one can dry, the sun's ultra-violet rays have a sterilising effect which slows the growth of some micro-organisms, and sun-dried fruit usually retains an attractive colour.

The disadvantages are inclement weather, and even in the best of conditions, this method is slow, taking four to five days compared with no more than eight hours in a properly-constructed drier using heat, whether electrical, kerosene, etc.

The theory of drying requires not only heat but the moisture driven off must be absorbed, into the air and dispersed. The requirement, therefore, is for warm, very dry air. This poses a problem in FNQ where the relative humidity is usually too high for normal air flow to carry off this moisture. Such high humidity is likely to cause problems with mould, both with sun-drying and with artificial driers that rely solely on convection currents to disperse moist air.

Similar problems could well be encountered with solar driers, which are now becoming quite popular and relatively easy to build. It seems therefore that the ideal drier for this climate is likely to be of the cabinet type with some artificial source of heat, preferably thermostatically-controlled, with a forced air circulation.

I have studied a number of plans and hope to obtain further ones from the USA shortly.

DATE: March 1980

* * * * * * * * * * * * *