. we 
28 BULLETIN 1022, U. S. DEPARTMENT OF AGRICULTURE. 
From the curves it is obvious that only a short exhaust is necessary 
for peas, two to four minutes being ample if sealing follows imme- 
diately. Emphasis must be laid on prompt sealing, however, as the 
air of the head space cools more rapidly than the material, and unless 
sealing is effected at once abnormal or too high pressures are de- 
veloped during the processing and too low vacuums are obtained on 
cooling. 
The cooling curves are of interest in that they show again how, 
in material like peas, the starch and other substances which are 
cooked out alter the viscosity of the liquor, causing the form of the 
cooling curves when temperatures are reversed to vary considerably 
from that of the heating curves. This is more marked in peas than 
in string beans. The curves also show how’the viscosity 1s increased 
eae 
TEMPERATURE IN DEGREES CENTIGRADE 
TIME IN MINUTES 
Fig. 16.—Experimental time-temperature curves for peas in No. 8 tin cans, starting at 
different uniform temperatures and processed at 100°, 116°, and 121° C. Curve for 
can starting: A, At 24° C. and processed at 100° C.; a, at 243° C. and processed at 
116° C.; a’, at 242° C. and processed at 121° C.; C, at 80° C. and processed at 100° 
C.3 ¢, at 80° C. and processed at 116° C.; ce’, at 80° C. and processed at 121° C. 
by the higher processing temperatures. The viscosity will also be 
affected by the degree of maturity of the peas and the length of the 
processing period. 
Figure 16 shows curves for the No. 3 can and illustrates how, be- 
cause of the rapidity with which temperature changes occur, process- 
ing periods for No. 2 and No. 3 cans need differ but little; that is, 
four or five minutes. 
There are several factors which will make the temperature change 
during processing vary slightly. If in any way a number of peas 
get broken the starch will come out of these more readily and will 
make the rate of change of temperature slightly slower. The more 
mature the peas the greater will be this effect. The proportion of 
peas to liquor will have a small effect also. If the proper quantity 
