Podcast
Questions and Answers
What is the purpose of blanching vegetables as a pre-treatment for dehydration?
What is the purpose of blanching vegetables as a pre-treatment for dehydration?
- To remove natural enzymes (correct)
- To add moisture
- To increase hardness
- To enhance bacterial growth
Which post-dehydration treatment involves holding dehydrated foods for moisture equalization before packing?
Which post-dehydration treatment involves holding dehydrated foods for moisture equalization before packing?
- Sweating (correct)
- Fumigation
- Inspection
- Screening
What is the purpose of sulphuring whole or pieces of fruits in a closed chamber before dehydration?
What is the purpose of sulphuring whole or pieces of fruits in a closed chamber before dehydration?
- To enhance oxidation
- To reduce moisture content
- To promote mould growth
- To prevent darkening (correct)
How are the unwanted size pieces of dried products removed in the post-dehydration stage?
How are the unwanted size pieces of dried products removed in the post-dehydration stage?
Which treatment is used to fix insects and their eggs after dehydration?
Which treatment is used to fix insects and their eggs after dehydration?
What effect does uneven water removal during drying have on food materials?
What effect does uneven water removal during drying have on food materials?
What is the main cause of case hardening in dried products?
What is the main cause of case hardening in dried products?
How can you determine the dryness of dried fruit?
How can you determine the dryness of dried fruit?
What is the recommended moisture content for dried vegetables?
What is the recommended moisture content for dried vegetables?
Which of the following is NOT a type of dried product mentioned in the text?
Which of the following is NOT a type of dried product mentioned in the text?
What is one of the causes of spoilage of dried products mentioned in the text?
What is one of the causes of spoilage of dried products mentioned in the text?
How long does it typically take to dry larger juicy fruits like peach or apricot halves?
How long does it typically take to dry larger juicy fruits like peach or apricot halves?
What slows down the drying process during the initial stages of drying food products?
What slows down the drying process during the initial stages of drying food products?
What does the establishment of normal equilibrium relative humidity (ERH) indicate?
What does the establishment of normal equilibrium relative humidity (ERH) indicate?
What factors affect the drying rate of food products in a drying process?
What factors affect the drying rate of food products in a drying process?
Why does water tend to retain in the center of food during the establishment of a dried thick layer?
Why does water tend to retain in the center of food during the establishment of a dried thick layer?
How does the establishment of a dried thick layer affect heat transfer during the drying process?
How does the establishment of a dried thick layer affect heat transfer during the drying process?
Which type of drying method involves using solar energy for the drying process?
Which type of drying method involves using solar energy for the drying process?
Study Notes
Dehydration and Dried Products
- High surface temperature and unbalanced drying can cause dry skin, leading to case hardening
- Enzymatic browning can occur due to poor blanching
- Caramelization of sugars can occur due to excess heat
- Loss of volatile flavor constituents and partial loss of essential nutrients like Vitamin C can occur during dehydration
Determining Dryness
- Fruits: 6 hours for thin/small pieces, 10-12 hours for larger juicy fruits like peach or apricot halves
- Dried fruit will feel leathery, won't stick to itself, and have no visible moisture
- Vegetables: dry until brittle or "crisp" with low moisture (10%)
Dried Products
- Examples: dried figs, prunes, resins, chenpi (sun-dried mandarin peels), dried peaches, dried apricots, dried strawberries, dried mango slices, sun-dried potato chips, dried tomatoes, dried onions, dried mushrooms
Spoilage of Dried Products
- Defects:
- Moulding: high product moisture, above ERH; prevention: reduce moisture content, pack in hermetic airtight packages
- Infestation: presence of larvae or insects in dried products; prevention: storage room disinfection with fumigants, disinfection by heat (60-65°C) of products before packing
- Browning: chemical reaction; prevention: reduce water content, store at low temperature, sub-atmospheric dehydration
Pre- and Post-Dehydration Treatments
- Pre-treatments:
- Blanching: inactivate natural enzymes, remove hardness, reduce bacterial load
- Sulphuring: check growth of mould, act as preservative/antimicrobial agent, prevent oxidation and darkening
- Fruit juice dip, honey dip, syrup blanching
- Post-dehydration treatments:
- Sweating: hold dehydrated foods for equalization of moisture before packing
- Screening: remove unwanted size of pieces of products
- Inspection: remove discolored pieces manually
- Fumigation: fix insects including their eggs
Changes During Drying
- Food materials do not have perfect elasticity, and water is not removed evenly throughout food as it is dried, causing shrinkage
- Heat and mass transfer: heat into product, moisture out of product
- Development of dried thick layer: moisture from surface of food is removed, later it becomes slow due to development of dried thick layer
- Establishment of moisture gradient: dried thick layer acts as insulation against rapid heat transfer, water retains in the centre of food
Factors Affecting Drying Rate
- Temperature
- Velocity of air
- Surface area
- Size of product
- Tray load
- Relative humidity of air
- Atmospheric pressure and vacuum
Types of Drying
- Sun drying, solar drying
- Atmospheric drying: batch (kiln, tower & cabinet driers) and continuous (tunnel, belt, belt trough, fluidized bed, foam mat, drum and microwave)
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Description
Learn about the signs of dry fruit such as surface temperature, enzymatic browning, caramelization, and loss of nutrients and flavor. Understand the time needed for drying different types of fruits and how they should feel when properly dried.
