Industrial practice for reducing defective sterile milk products produced using overpressure rotary retorts

Muhamad Wahyu Pamuji, Eko Hari Purnomo, Azis Boing Sitanggang


Indonesian consumers are fond of commercially sterilized milk as indicated by increasing product sales. High demand for products intensifies the need to increase productivity, generally achieved by minimizing product defects. This study aimed to reduce the number of defects in commercially sterilized milk produced using overpressure rotary retorts. Based on Pareto analysis, the percentage of defective products was 5.14% of which 2.37% were dented bottles. A cause-effect diagram (Ishikawa Diagram) was used to find the root cause of dented bottles. The pressure difference between the retort chamber (external pressure) and inside the product packaging (internal pressure), and the number of bottles stacked inside the retort basket (bottle density) were found as major factors for causing dented bottles. The internal pressure was 1.20 bar higher than the external pressure. By reducing the pressure difference to 0.40 bar, the percentage of dented bottles could be reduced to 0.79%. Applying the low-est bottle density (73% of the retort basket area occupied by bottles) during the sterilization process could decrease the number of dented bottles, however, it also increased the appearance of striped lids. The best conditions for sterilization (pressure difference = 0.40 bar; number of bottles/basket = 1938 bottles) which were used in the three-month full-scale production trial reduced the percentage of defective products from 5.14% to 2.24% of which 0.76% were dented bottles. Setting the retort pressure at 2.80 bar could avoid 52,920 defective bottles of commercially sterilized products per month.


Commercially sterilized milk; product defects; dented bottles; overpressure rotary retorts; sterilization

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