National University of Singapore
Food Science & Technology
Determination of freezing curve for pear
Materials:
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Blast freezer
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Pear
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Knife
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Chopping board
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Moisture analyser
Objectives:
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To compare the experimentally determined freezing time of two slab samples of different size with the theoretical freezing time obtained from predictive equations (Plank’s Equation and Nagaoka’s Equation).
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To determine the convective heat transfer coefficient using the experimental freezing time.
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To investigate the effect of the pear slab sample size on freezing time.
Methodology
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Cut a slab from food sample and trim it into well-defined geometry with an approximate dimension of 4.0 cm x 4.0 cm x 1.5 cm.
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Record down the mass and dimensions of the trimmed slab and determine its density.
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Measure the moisture content of the food sample using a moisture analyser.
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Insert a thermocouple which is connected to a computerised measurement system into the geometric centre of the slabs prior to the freezing process.
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Leave the other tip of the thermocouple exposed in the freezer for the measurement of the freezing medium temperature.
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Record down the initial product and freezing medium temperatures.
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Place the slab sample into the freezer and start the freezing process.
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Monitor the time-temperature data tabulated by the computerised system during the entire freezing process until the temperature of the slab reaches -10°C.
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Repeat the above procedures for another slab sample with an approximate dimension of 2.0 cm x 2.0 cm x 1.5 cm.
(Top) Demonstration video on estimating the freezing time of pear samples