38 BULLETIN 1022, U. S. DEPARTMENT OF AGRICULTURE. 
SWEET POTATOES. 
PRESSURE STUDIES. be 
Tn the tests upon sweet potatoes the material used was in the form 
of “pie stock,” prepared by washing the potatoes, steaming until 
’ done, peeling, and then passing them through a food chopper to give 
a uniform consistency. The material was then weighed into the test 
cans, 600 grams being used in the No. 2 and 1,000 grams in the No. 3 
can. After the can 
roa ea and contents were 
brought to a uniform 
desired temperature, 
the tests were per- 
formed in the usual 
way. Figure 25 
shows the time-pres- 
sure curves for sweet 
potatoes in No, 2 cans 
sealed at the initial 
temperatures of 25° 
(0°, and 8097 and 
i Er“ i, ino Beef ToT on ab al processed for 120 
{foe minutes at 116° C., 
pf ca an eee rea ues and figure 26 shows 
WV eVholc of so] leeamatos tet [teed | the curves for No. 3 
A oe Se eee Saleen cans tested in the 
| 2 
The outstanding 
pee ee ee 
’ | _ for sweet potatoes are 
50 60 7 
TOME WA MINUTES much the same as for 
Fig. 25. ans bareaeatal time-pressure curves for sweet pota- 
toes in the form of pie stock in No. 2 tin cans, sealed sweet COPS 
at different uniform temperatures and processed for 2 The initial sudden 
hours at 100° C., 116° C., and 121° C. Curve for can . = = 
sealed: A, At 25° C. and processed at 100° C.; a, at 25° HeSe ts ie Swe. does 
C. and processed at 116° C.; a’, at 25° C. and processed not reach sO high a 
at 121° C.; B, at 70° C. and processed at 100° C.; b, at : . : 
70° C. and processed at 116° C.; 6’, at 70° C. and proc- point are the Corr: 
essed at 121° C.;.C, at 80° C. and processed at 100° C.; OWING to smaller 
C; at 80° C. and processed at 116° Cs G5 at 80° C. and head space. That 
processed at 121° C. 
ind 
n 
wy 
> 
nw 
N_ 
PRESSURE IN POUNDS PER SQUARE INCH 
this sudden rise is 
due to the expansion of the air of the head space is clearly shown 
by the fact that the curves following this initial rise begin their more 
gradual ascent at approximately the same point, later diverging ac- 
cording to the sealing temperature employed. 
The rise in pressure continues throughout the processing period, 
corresponding in some degree to the rate of temperature change 
within the can, but not due entirely to this. The pitch of the curves 
