Moisture Relationships in Physical Properties of Biological Materials

1. Lecture 6 – Moisture Relationships BAE2023 Physical Properties of Biological Materials Lecture 5

2. Lecture 6 – Moisture Relationships Amount of moisture affects the following: Density: particle density decreases with increasing moisture content Force-deformation characteristics Thermal conductivity Heat capacity Electrical resistance: lower resistance with higher moisture content BAE2023 Physical Properties of Biological Materials Lecture 5

3. Lecture 6 – Moisture Relationships Amount of moisture affects: Fruits and veggies: 70-95% mc Grains, seeds, dry food products: < 14% Meats: 60-80% MC influences market value BAE2023 Physical Properties of Biological Materials Lecture 5

4. Lecture 6 – Moisture Relationships Three concepts: Equilibrium mc Water activity Water potential BAE2023 Physical Properties of Biological Materials Lecture 5

5. Lecture 6 – Moisture Relationships Equilibrium mc Moisture transfers from product to air during drying. EMC describes the final moisture reached during drying of lower moisture food products, grains, seeds Affects rate of drying Explains mold growth in grain BAE2023 Physical Properties of Biological Materials Lecture 5

6. Lecture 6 – Moisture Relationships Water Activity Describes rate of deterioration Water Potential Describes the effect of moisture loss or gain on volume change and force deformation behavior of fruits and veggies BAE2023 Physical Properties of Biological Materials Lecture 5

7. Lecture 6 – Moisture Relationships Determining Moisture Content (VERY IMPORTANT) Wet Basis % of total weight with water Dry Basis Ratio of water weight to dry matter weight One can be calculated using the other BAE2023 Physical Properties of Biological Materials Lecture 5

8. Lecture 6 – Moisture Relationships Equations: Wet basis Dry basis BAE2023 Physical Properties of Biological Materials Lecture 5

9. Lecture 6 – Moisture Relationships Equations: Conversion Wet to dry Dry to wet BAE2023 Physical Properties of Biological Materials Lecture 5

10. Lecture 6 – Moisture Relationships Wet basis example 700 kg of wheat contains 84 kg of water. What is the MCw ? BAE2023 Physical Properties of Biological Materials Lecture 5

11. Lecture 6 – Moisture Relationships Dry basis example 950 kg of oats contains 105 kg of water. What is the MCd ? BAE2023 Physical Properties of Biological Materials Lecture 5

12. Lecture 6 – Moisture Relationships Conversion example Convert the wheat and oat examples above BAE2023 Physical Properties of Biological Materials Lecture 5

13. Lecture 5 – Moisture Relationships “How much water did we lose” example 750 kg of canola is dried from 17% MCw to 12% MCw How much water is removed during the drying process? BAE2023 Physical Properties of Biological Materials Lecture 5

14. Lecture 6 – Moisture Relationships Another example A bin holds 2000 kg of wet grain containing 500 kg of water. This grain is to be dried to a final MC of 14% (wb). What are the initial and final moisture contents of the grain (wb and db)? How much water is removed during drying? BAE2023 Physical Properties of Biological Materials Lecture 5

15. Lecture 6 – Moisture Relationships Another example An elevator has 14,000 kg of wheat at 12% MCw and 25,000 kg of wheat at 17% MCw. The manager has a rule that all stored wheat must be below 15% MCw. If the wheat is mixed together, will it meet the storage criteria? BAE2023 Physical Properties of Biological Materials Lecture 5

16. Lecture 6 – Moisture Relationships Another example A bag containing 1.5 kg of popcorn has been stored in the cabinet for a long time. When heated appropriately, only a few kernels popped. Testing showed that the MCw was 9%. Popcorn pops best at 13%. How much water should be added to bring it to this moisture? BAE2023 Physical Properties of Biological Materials Lecture 5