–Amount of moisture affects the following:• Density: particle density decreases with increasing moisture contentLecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 61increasing moisture content• Force-deformation characteristics• Thermal conductivity• Heat capacity• Electrical resistance: lower resistance with higher moisture content–Amount of moisture affects:• Fruits and veggies: 70-95% mc•Grains, seeds, dry food products: < 14%Lecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 62•Grains, seeds, dry food products: < 14%• Meats: 60-80%• MC influences market value–Three concepts:• Equilibrium mc•Water activityLecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 63•Water activity• Water potential–Equilibrium mc• Moisture transfers from product to air during drying. Lecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 64during 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– Water Activity• Describes rate of deterioration–Water PotentialLecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 65–Water Potential• Describes the effect of moisture loss or gain on volume change and force deformation behavior of fruits and veggies– Determining Moisture Content (VERY IMPORTANT)•Wet BasisLecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 66•Wet Basis–% of total weight with water• Dry Basis –Ratio of water weight to dry matter weight• One can be calculated using the other– Equations:total dry wetW W W= +Lecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 67• Wet basis• Dry basis100 100water waterWtotal water dryW WMW W W = = + 100waterdrydryWMW = – Equations:• Conversion–Wet to dry100wMM = Lecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 68–Wet to dry– Dry to wet100100100100wdwdwdMMMMMM = − = + – Wet basis example700 kg of wheat contains 84 kg of water. What is the MCw ?Lecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 69What is the MCw ?– Dry basis example950 kg of oats contains 105 kg of water. What is the MCd ?Lecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 610What is the MCd ?–Conversion exampleConvert the wheat and oat examples aboveLecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 611– “How much water did we lose” example750 kg of canola is dried from 17% MCw to 12% MCw Lecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 61212% MCw How much water is removed during the drying process?–Another exampleA bin holds 2000 kg of wet grain containing 500 kg of water. This grain is to be dried to Lecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 613500 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?–Another exampleAn elevator has 14,000 kg of wheat at 12% MCwand 25,000 kg of wheat at 17% MCw. The manager has a rule that all stored Lecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 614MCwand 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?–Another exampleA bag containing 1.5 kg of popcorn has been stored in the cabinet for a long time. When heated appropriately, only a few Lecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture 615been stored in the cabinet for a long time. When heated appropriately, only a few kernels popped. Testing showed that the MCwwas 9%. Popcorn pops best at 13%. How much water should be added to bring it to this moisture?–Homework...See Lecture 6Lecture 5 – Moisture Relationships1/25/2010 BAE2023 Physical Properties of Biological Materials Lecture
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