Experimental design with pellet heating time of 1.00, 1.33, 1.67, 2.00, 2.33, 2.67, 3.00, 3.33, 3.67, and 4.00 min was studied to investigate the effects of pellet heating time on the physical properties (expansion ratio, density and breaking strength) of vacuum-puffed Yukwa. The size and shape of vacuum-puffed Yukwa varied with respect to the pellet heating time.As pellet heating time increased, a values and b values tended to increase. The maximum expansion (4.626) with the lowest bulk density (0.112) was obtained at 3.33 min heating time, whereas the minimum expansion (2.954) with the highest bulk density (0.208) was found at 1 min. The breaking strength of vacuumpuffed Yukwa decreased significantly as the pellet heating time increased. Overall, the heating time had significant impacts on the physical properties of vacuum-puffed Yukwa.

The effects of pellet moisture content on physical properties (expansion ratio, density and breaking strength) of vacuum-puffed Yukwa (non-oil puffed Yukwa) were investigated in this study. The Yukwa was made from the waxy rice steeped at 25 and 30oC for 3, 5 and 10 days with pellet drying times (6, 8 and 10.5 hr), respectively. As the drying time increased from 6 to 10.5 hr at 50oC, the highest value of pellet moisture content (29.4%) was found in the samples made from the steeped waxy rice at 25oC for 5 days after 6 hr drying, while the lowest value (16.3%) was found at 25oC for 3 days after 10.5 hr drying. Both redness and yellowness values of vacuum-puffed Yukwa increased as the drying time increased. The expansion ratio of Yukwa was greatly affected by drying time, ranging from 2.07 (26.8% pellet moisture content) to 7.01 (24.0% pellet moisture content). From the data, it was concluded that the pellet moisture content had a significant influence on the physical characteristics of vacuumpuffed Yukwa. With vacuum puffing condition of 3 min heating and 2 min puffing, the pellets with about 25% moisture content showed higher expansion ratio, and lower density and breaking strength.