PROGRESS IN THE DEHYDRATION INDUSTRY. 
flavour very closely approximating that of the fresh fruit, and when 
placed in water more nearly resume the texture of fresh fruit. The 
products of dehydration plants are sulphured much less, and contain, 
on an average, 5 per cent. less water than the ordinary dried or 
evaporated fruit. 
. A rather higher moisture content has always been permissible in 
fruits, due to the high acid and sugar contents, which tend to act as 
preservatives. In the ordinary dried or evaporated fruits, the moisture 
content is often high enough to be favorable to the development of 
moulds. The moisture content of the “dehydrated” fruit is generally - 
under 20 per cent. 
Sulphuring* of fruits has long been practised on the Pacific coast. 
Sulphur dioxide fumes are used to bleach the fruit before drying, and 
the retained sulphurous acid acts as a preservative after drying. 
Sulphuring, no doubt, facilitates handling of the fruit, but heavy 
sulphuring is very objectionable. The sulphurous acid obscures and 
destroys the delicate fruit flavour, and in heavily sulphured products 
we have left only a tart or sweet taste. 
The dehydration plants use sulphur dioxide as a bleaching agent only, 
and not as a preservative. The products are sulphured very lightly, 
and the sulphurous acid is removed from the products in the process 
“of drying. The fruit is generally given a short steaming before drying, 
and this steaming, together with the lower moisture content, assures a 
product of good keeping qualities. 
There has been little or no change during the past year in the drying 
equipment of existing plants. Two attempts were made to use a moving - 
belt dryer for dehydration of fruits and vegetables. One attempt was 
wholly unsuccessful, and the other only partially successful. <A. plant 
must be able to handle a variety of products—both fruit and vegetables 
—in order to prolong the operating season, and thus cut down the over- 
head expense. <A dryer, using trays, is essential for some products, 
notably the softer fruits, and therefore any type of dryer in which trays 
are eliminated will have a very limited use. In one essential, all of 
the dehydration equipment is similar—air is used as a medium for 
conveying heat to the product and carrying away the evaporated 
moisture. In the simplest type, atmospheric air is heated to the desired 
temperature, passed over the product, and discharged. In other types, 
the relative humidity of the air is raised (in some cases as high as 60 
per cent.) by re-circulating the air. The majority of dryers may be 
classed as tunnel dryers, and many other drying units are essentially 
modifications of the tunnel type. The kiln type is, of course, an excep- 
tion. 
Vacuum dryers have been used in various industries for some years, 
and are at present used for the drying of milk. Vacuum has long been 
a laboratory aid to the chemist in drying food materials. While fruit 
and vegetables of good quality can be produced in a vacuum dryer, their 
quality is not superior to those dried in a current of air. Further, the 
most expensive type of dryer using air as a medium of evaporation is 
much less expensive per unit than vacuum dryers. 
363 
