August, 1918 
WISCONSIN HORTICULTURE 
171 
the interior of the material, when 
the process will, of course, be slow- 
ed and stopped by the drying out 
of an outside layer, which will then 
retard the escape of moisture from 
the tissues beneath it. 
There arc therefore two ways in 
which the rate of drying can be in- 
creased ; namely, by increasing the 
temperature of the air or by quick- 
ening its rate of movement over 
the material to be dried. Econom- 
ical drying is secured by combin- 
ing 1 he and forcing currents 
of heated air over the material at 
such temperature and rate of 
movement as will remove moisture 
from the surface as rapidly as it 
can move outward from the inter- 
ior of the fruit or vegetable being 
dried. When this point has been 
reached, any expenditure of heat 
in further warming the air or of 
force in driving it is, of course, 
wasted. 
Generally speaking, flavor and 
cooking quality are best preserved 
by rapid drying. Fruits and vege- 
tables are living things; when their 
flesh is opened up to the air, as 
occurs in peeling and slicing, a 
number of chemical changes in the 
tissues immediately begin. If the 
material is to retain its natural ap- 
pearance, color, and flavor, these 
must be checked. Some of these 
changes produce darkening and 
discoloration of the tissues; others 
break down the pigments present, 
causing the fading of the charac- 
teristic colors of the material ; and 
still others affect the flavoring sub- 
stances present, producing decrease 
or loss of the constituents which 
give the fruit or vegetable its char- 
acteristic flavor. Other accompany- 
ing but slower changes result 
in the partial destruction of the 
sugars and proteins of the mater- 
ial, sometimes accompanied by the 
production of new and undesirable 
flavors and odors. While these 
changes are in parts spontaneous, 
many lower organisms, universally 
present in the air and upon food- 
stuffs — bacteria, yeasts, and molds 
— which produce similar but much 
more rapid decomposition, are 
certain to begin growth in the ma- 
terial as soon as the removal of the 
protecting peel gives them access 
lo its interior. Consequently, proc- 
esses of decomposition begin as 
soon as the fruit or vegetable is 
opened to the air and will continue 
until the greater part of the mois- 
ture present is removed unless spec- 
ial means are employed to arrest 
them. This decomposition would be 
immediately stopped by raising the 
temperature of the material to 
175° or 185° F., but it is not pos- 
sible to do this without causing in- 
jury. The rapid heating to this 
temperature m ary air of freshly 
cut slices of a succulent fruit or 
vegetable causes bursting of the 
cell membranes by t mansion of 
their contents and permits the es- 
cape of water which carries with it 
dissolved sugars, salts, and flavor- 
ing substances, thus reducing both 
the palatability and the food value 
of the product. Consequently, only 
moderate temperatures can be em- 
ployed, and unfortunately all, or 
practically all, the changes under 
discussion are not only allowed to 
continue but are actually hastened 
when the temperature of the fresh 
water-filled material is raised to 
the limit beyond which bursting 
and dripping will occur. To ar- 
rest these changes and to preserve 
the natural colors and flavors of 
the material it is necessary to re- 
sold either to blanching or sulphur- 
ing, both of which are discussed 
elsewhere. 
It follows from the foregoing 
statement that rapid drying can 
not be secured by the employment 
of high temperatures with fresh 
water-filled material. Nor can ma- 
terial already partially dry be sub- 
jected to high temperatures, as 
scorching and charring will then 
occur. The best temperature for 
drying is therefore the highest 
which can be employed without 
danger of injury in either of these 
ways, since the drying will thus be 
made most rapid. What this high- 
est possible temperature may be is 
determined in the case of any par- 
ticular fruit or vegetable by its 
physical structure, chemical com- 
position, and water content. As 
the different fruits and vegetables 
show very wide variations in these 
respects, there is no single best 
temperature for general use with 
the various products; heat treat- 
ment which would be perfectly safe 
with potatoes or carrots would be 
utterly ruinous if applied to such 
fruits as raspberries and peaches. 
For this reason it has been neces- 
sary to determine experimentally 
for each of the different materials 
the range of temperatures which 
may be employed without injury. 
These are given on subsequent 
pages. The operator of a drier 
should be provided with a depend- 
able, accurate thermometer which 
should be placed in the drier and 
kept under frequent observations, 
as any attempt to trust to inex- 
perienced judgment as to tempera- 
tures in the drier is likely to result 
in damage to the material. 
In drying any food material it 
is absolutely indispensable that 
provision be made for the prompt 
Continued on page 176 
