hy 
DEHYDRATION OF FRUITS AND VEGETABLES 25 
per cent relative humidity (fig. 8) are 0.0598 and 0.0026, respectively, 
the air required, in cubic feet per minute, is as follows: 
8,690 
35 X [ (0.0598 x 0.24) + (0.0026 x 0.475) ] 
VELOCITY OF AIR MOVEMENT 
= 16,000 
As previously estimated, the tunnel will have 25 square feet of 
free cross-sectional area. The velocity of movement of 16,000 cubic 
feet of air per minute through the tunnel therefore is ae or 640 
feet per minute. 
HUMIDITY AT AIR OUTLET END OF TUNNEL 
The air entering the tunnel at 160° F. and 20 per cent relative 
humidity contains (fig. 8) 0.0598 pound of dry air and 0.0026 pound 
of water vapor per cubic foot. Into 16,000 cubic feet of this mixture 
is evaporated 6.32 pounds of water vapor. Thus, » Or 
6.32 
16,000 
0.0004 pound of water vapor, would be associated with the weight of 
dry air and water vapor in 1 cubic foot of the original mixture. 
Disregarding the leakage of air into or out of the drying chamber, 
the air leaving the tunnel would contain 0.0026+0.0004, or 0.003 
pound of water vapor, associated with 0.0598 pound of dry air, or 
0.003 
0.0598 
125° F. containing 0.050 pound of water vapor per pound of dry air 
has 56 per cent relative humidity (fig. 9). 
END POINT OF DEHYDRATION 
» or 0.050 pound of water vapor per pound of dry air. Air at 
Dehydrated fruits and vegetables should have a uniform moisture 
content low enough to inhibit undesirable microbic and chemical 
changes within the food and they should be free from any part of the 
life cycle of moths or other insects. The moisture content of dehy- 
drated foods directly controls deterioration within the food, and the 
protection afforded by sulphuring or blanching will not prevent 
insufficiently dried products from soon becoming unfit for use. 
Dehydrated products having a low moisture content are not readily 
attacked by insects. In the long run the additional protection 
afforded by a low moisture content will more than make up to the 
producer the loss resulting from the longer drying time and greater 
weight shrinkage involved. To assure best keeping qualities the 
moisture content of fruits containing much sugar should not exceed 
15 to 20 per cent, while that of other fruits and vegetables should 
not exceed 5 to 10 per cent, the preference in both cases being for 
the lower percentage. 
The texture or ‘‘feel”’ of products is a guide in determining when 
the proper stage of dryness has been reached. At a given moisture 
content products usually feel softer when hot than after they have 
been cooled, and often they feel softer after standing until the mois- 
ture has become evenly distributed throughout the pieces than when 
first cooled. 
A rough test for moisture in dried fruits is to take up a double 
handful, squeeze it tight into a ball, and release the pressure. If the 
