Pepe ayer pc 
~e os So Set age 
10 BULLETIN 1335, U. S. DEPARTMENT OF AGRICULTURE 
‘One type of steam chamber consists of a tight room big enough to 
hold a loaded truck (fig. 3). On at least two opposite walls of the 
chamber are placed perforated steam pipes about 12 inches apart. 
In another type (fig. 4) the steam chamber consists of an elongated 
box similar in construction to the canners’ exhaust box, but narrower 
and longer. An endless chain conveying the loaded trays passes 
through the box, where steam jets are placed at frequent intervals 
at the top and at the bottom. 
Blanching by hot solution is not practiced extensively. The only 
type of apparatus used for this purpose consists of a conveyor in 
which the material is carried through a bath kept hot by steam coils. 
Some of the product is wasted in passing through the bath, and tray- 
ing is difficult after this treatment. 
SULPHURING 
Light-colored fruits are sulphtred in order to prevent discolora- 
tion during and after drying and to facilitate drying by destroying 
the capacity of the cell membranes to limit the passage of water 
through them. It is believed that sulphuring kills and plasmolyzes 
the cells and makes permeable the semipermeable cell membrane, 
thus facilitating the diffusion of water from the interior to the 
surface. 
When the general plan of operation makes it desirable, the fruit 
on trays is “‘sulphured”’ in af inclosed chamber, provided with an 
entrance for the sulphur gas and an exit for a draft (fig. 3). The 
chamber is usually large enough to hold one or two loaded trucks. 
Preferably the sulphur is burned in from three to six shallow pans 
stacked one above the other in zigzag formation. This method 
gives a large quantity of sulphur dioxide in a comparatively short 
time. Sometimesasulphur stoveis placed outside the chamber, and 
the sulphur fumes are carried into the chamber by flues. 
Another type of sulphuring apparatus is an elongated box, in which 
the fumes, conducted to the box from an outside source, act on the 
fruit as it passes through the box on a wooden slat conveyor. The 
speed of the conveyor may be regulated to give the proper duration 
of time for the sulphuring. | 
Dehydrated fruits are oversulphured much less frequently than 
sun-dried fruits because a shorter period of exposure is adequate, 
so that they rarely contain more than 70 milligrams of free sul- 
phur dioxide per kilogram. Occasionally, however, dehydrated fruits 
have been so heavily sulphured that they have a flavor which many 
people dislike. Sulphuring, therefore, should always be as light as 
possible. 
DRYING 
EQUIPMENT 
Driers are of two general types, vacuum and air. Air driers are 
further classified as natural-draft and forced-draft. Stack and kiln 
driers belong to the natural-draft type; endless-belt, compartment, 
and tunnel driers, to the forced-draft type. Almost all types are 
covered, in part at least, by patents. Morar patented special types 
