Sous vide lamb shank modelling and process improvement
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The optimum production is important for the manufacture companies as it allows the optimistic using of capital and ensures the competitiveness of product in market. This thesis explores the options to optimise the existing sous vide lamb shank process, and subsequently, the product quality. The thermal history of a model laboratory process and the existing commercial process were profiled by physical and computer models. The measured results showed that a higher temperature variation present in the commercial process, compared to the well controlled model laboratory process. The temperature variation impacted the textural properties of the products, as there was no significant difference between the commercial-processed shanks in different weight ranges, whereas the size effect was marked in the laboratory-processed equivalents, where the heavier shanks were more difficult to chew. FPM and FlexPDE were used to model the cooking-cooling process. The FPM model showed that the shank temperature was generally lower in the commercial products, and caused these products was more difficult to chew. The FlexPDE model was a poor predictor of the temperature profile of lamb shank during the cooking process, due to the failure to the thermal conductivity of bone in the model. However, the model pointed the importance of bone as a conductor of heat from the ends of the shank to the meat surround. The cooking time was shortened to 4.5 hours from the standard 5.5 hours, to explore the potential of shortening cooking time. The physical measurements on shanks cooked in the laboratory for the two different times showed that longer time caused higher cooking loss, however, the cooking time did not affect the mean muscle shrinkage, and the variations were low. The commercial products had similar mean shrinkage value to the laboratory shanks, but the variation was much higher, which again suggested the higher temperature variation in the commercial process. In addition, the comparison of texture between these three shanks showed that the textural values of the commercial-processed shanks were similar to the 4.5-hour laboratory-processed shanks, which were higher (more difficult to chew) than the 5.5-hour laboratory equivalents. The consumer test suggested that the 4.5-hour laboratory-processed shanks were preferable to the 5.5-hour equivalents, and the over-tenderisation may be the main reason for the less attractiveness of the 5.5-hour shanks. The microbiological tests showed that the existing start-point of the material, the existing cooking-cooling process and the subsequent frozen storage could effectively reduce the bacterial loads inside the product package. Recommendations were discussed that aim to reduce the temperature variation in the existing commercial process. The first recommendation was reducing the product heat load by increasing the mean temperature of the shanks prior to loading. This could be achieved by tempering the packed shanks in an equilibration bath that contains mains supply water for a certain time. This would ensure a more even temperature distribution when the products are loaded into the cooking bath, consequently reduce the required cooking time/energy consumption. Improving the heating capacity of the cooking system was another way to reduce the temperature variation, which could be achieved by increasing the heating capacity of the cooking bath and increasing the circulation of the bath fluid. The heating capacity of the cooking bath could be improved by redesigning the heating system of the bath and increasing the effectiveness of the insulation surround. And the circulation could be increased by applying either pump recirculation or mechanical stirrer. A more detailed evaluation of the cooking bath was also recommended, as it would profile the temperature history in the bath more accurately.