38 



BULLETIN 1022, U. S. DEPARTMENT OF AGRICULTURE. 



SWEET POTATOES. 



PRESSURE STUDIES. 



In 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 

 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°, 

 70°, and 80° and 

 processed for 120 

 minutes at 116° C, 

 and figure 26 shows 

 the curves for No. 3 

 tested in the 



cans 



same manner. 



The outstanding 

 features of the curves 

 for sweet potatoes are 

 much the same as for 

 sweet corn. 



The initial sudden 

 rise in pressure does 

 not reach so high a 

 point as in the corn, 

 owing to smaller 

 head space. That 

 this sudden rise is 



Fig. 25. — Experimental time-pressure curves for sweet pota- 

 toes in the form of pie stock in No. 2 tin cans, sealed 

 at different uniform temperatures and processed for 2 

 hours at 10O° C, 116° C, and 121° C. Curve for can 

 sealed : A, At 25° C. and processed at 100° C. ; a, at 25° 

 C. and processed at 116° C. ; a', at 25° C. and processed 

 at 121° C. ; B, at 70° C. and processed at 100° C. ; 6, at 

 70° C. and processed at 116° C. ; 6', at 70° C. and proc- 

 essed at 121° C. ; C, at 80° C. and processed at 100° C. ; 

 c, at 80° C. and processed at 116° C. ; o', at 80° C. and 

 processed at 121° C. 



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 



