The Effect of Retort Processing Factors on the Severity of Film Surface Impression

Retort processing conditions of temperature, overpressure, and sterilization time were used to determine the impression depth on the pouch surface from contact with the retort rack during retort processing, also referred to as a waffling defect. Retortable flexible pouches were filled with 1,000 mL of water and processed in a horizontal water spray retort. A confocal laser scanning microscope was used to measure severity of the waffling defects. Data collected during this study showed that higher temperatures resulted in higher measured impression depth values (p<0.05) in all of the tested combinations. However, when the pouches were retorted at different temperatures, different effects of retort overpressure were observed. At a low temperature (111 deg. C), the higher overpressure resulted in higher severity of the waffling defects (p<0.05). In contrast, at a high temperature (131 deg. C), the higher overpressure resulted in lower severity of the waffling defects (p<0.05). When samples were retorted at different sterilization time settings, there was only one condition where a statistical difference in the impression depth values was observed (p<0.05). The longer sterilization time resulted in higher measured impression depth (p<0.05) only if the samples were retorted at a high temperature of 131 deg. C with a low overpressure of 26 psig. There was no statistical difference (p>0.05) in measured impression depth when samples were retorted at different sterilization time settings in other tested combinations. The difference in variance of the impression depth values between the samples retorted at different processing factor combinations was also studied. Processing factor combinations with a high temperature of 131 deg. C and a long sterilization time of 60 minutes, at any overpressure setting, resulted in a higher variance of waffling defect severity (p<0.05) compared to other combinations. The relationship between retort processing factors and waffling defect severity was explained using a prediction equation. The lack of fit of the proposed equation was not significant (p>0.05), while the hypothesis test (overall F-test) showed that the overall model was statistically significant (p<0.05). Therefore, the proposed equation is useful in predicting the average impression depth value when retort temperature, overpressure, and sterilization time are known. This study showed how retort processing factors affect the severity of waffling defects and proposed a method to predict the waffling defect severity. This information could allow pouch manufacturers to develop retortable pouches and food processors to create new retort processes to reduce waffling.