1. Lecture 6 – Moisture Relationships
12/9/2018
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
12/9/2018
BAE2023 Physical Properties of Biological Materials Lecture 5

3. Lecture 6 – Moisture Relationships
Amount of moisture affects:
Fruits and veggies: % mc
Grains, seeds, dry food products: < 14%
Meats: %
MC influences market value
12/9/2018
BAE2023 Physical Properties of Biological Materials Lecture 5

4. Three concepts: Equilibrium mc Water activity Water potential
Lecture 6 – Moisture Relationships
Three concepts:
Equilibrium mc
Water activity
Water potential
12/9/2018
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
12/9/2018
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
12/9/2018
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
12/9/2018
BAE2023 Physical Properties of Biological Materials Lecture 5

8. Equations: Wet basis Dry basis
Lecture 6 – Moisture Relationships
Equations:
Wet basis
Dry basis
12/9/2018
BAE2023 Physical Properties of Biological Materials Lecture 5

9. Equations: Conversion Wet to dry Dry to wet
Lecture 6 – Moisture Relationships
Equations:
Conversion
Wet to dry
Dry to wet
12/9/2018
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 ?
12/9/2018
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 ?
12/9/2018
BAE2023 Physical Properties of Biological Materials Lecture 5

12. Conversion example Convert the wheat and oat examples above
Lecture 6 – Moisture Relationships
Conversion example
Convert the wheat and oat examples above
12/9/2018
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?
12/9/2018
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?
12/9/2018
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?
12/9/2018
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?
12/9/2018
BAE2023 Physical Properties of Biological Materials Lecture 5