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Based on our experiments, we expected that pasteurized milk will last longer than raw milk. We also expected the High temperature Short Time Method would preserve the milk longer than the Low Temperature Holding method for pasteurization. Further research to expand on these result should include a control (such as water) for comparison. New research to build on these principals can also explore the other two methods: Ultra High Temperature Sterilization and Ultra High Temperature Pasteurization also Experiments to see if Ultra High Temperature Sterilization could have impacts on nutritional values.
High Temperature Short Time Method
1. Repeat steps 1-4 from above.
2. When the milk reaches a constant temperature of 161 degrees Fahrenheit (° F), set your stop watch to 15 seconds.
3. After 15 seconds, remove the double boiler system from the stove.
4. Repeat steps 7-8.
5. Label the test tube HTST (for High Temperature Short Time) with the tape and pen and place in a refrigerator set at 36 –38 ° F.
Observations
Low Temperature Holding Method
1. Turn on the stove to high heat.
2. Set up the boiler system by adding water until about 1 inch can be measured from the bottom of the lower pan.
3. Place the top pan over the bottom pan and add 30 mL of raw milk.
4. Place the double boiler system on top of the stove, and clip the thermometer to the top to measure the milk’s temperature.
5. When the milk reaches a constant temperature of 145 degrees Fahrenheit (° F), set your stop watch to 30 minutes.
6. After 30 minutes, remove the double boiler system from the stove.
7. Set the manual pipette to 20 mL and extract 20 mL of milk from the top pan.
8. Insert 20 mL of milk into a glass test tube and place a cork on top.
9. Label the test tube LTH (for Low Temperature Holding) with the tape and pen and place in a refrigerator set at 36 –38 ° F.
10. High Temperature Short Time Method
11. Repeat steps 1-4 from above.
12. When the milk reaches a constant temperature of 161 degrees Fahrenheit (° F), set your stop watch to 15 seconds.
13. After 15 seconds, remove the double boiler system from the stove.
14. Repeat steps 7-8.
15. Label the test tube HTST (for High Temperature Short Time) with the tape and pen and place in a refrigerator set at 36 –38 ° F.
The following experiment describes the method of pasteurizing and cooling milk at home. The materials involved include three 100 mL of raw (unpasteurized) milk, three 16 x 70 mm glass test tubes, three test tube lids, a clip thermometer, a stop watch, a manual pipette with three glass pipette attachments, a double boiler system, a stove, a roll of paper tape, a pen, and a refrigerator.
The glass test tubes and glass pipettes must be sterilized in boiling water before use. Old pipettes must NEVER BE REUSED. Handle the test tubes and glass pipettes with a sterile technique to avoid contamination.
Unpasteurized Raw Milk
1. Set the manual pipette to 20 mL and extract 20 mL of milk from the raw unpasteurized milk.
2. Insert 20 mL of milk into a glass test tube and place a cork on top.
3. Label the test tube RAW (for raw pasteurized milk) with the tape and pen and place in a refrigerator set at 36 –38 ° F.
The outcome of our experiment reflected our prediction, and we rejected our null hypothesis. The raw milk spoiled first, the LTH milk second, and the HTST last. The raw milk first began to show signs up spoiling on the 8th day with slow progression toward a solid state. After a few more days, a clear difference in saturation was observed, with what appeared to be slightly opaque water appearing at the bottom. Both LTH and HTST milks appeared unaffected. On the 16th day, the LTH milk appeared partially solid with cloudiness at the top. The raw milk developed more slightly opaque water at the bottom. The HTST milk appeared unaffected. On the 18th day, the raw milk formed more slightly opaque water on the bottom. The LTH milk developed a small amount of slightly opaque liquid about 2 centimeters (cm) above the bottom and the HTST milk appeared unaffected. On the 21st day, the raw milk developed a small amount of an amber color at the surface, and the LTH milk has a larger region slightly opaque water. The HTST milk appears thicker with a cloudy film layer developing on the surface.
The results indicate that pasteurized milk lasts longer than raw milk when refrigerated. The HTST method provides milk with a longer edible period than the LTH method.