1. Dehydration & concentration
Anna Kitchen
Shannon Hawkins
Morgan Modany

2. Three categories of processed foods
Dehydration/Rehydration
Concentration
Intermediate-moisture foods

3. Dehydration lowers the water content (oldest method)
artificial drying of food product under controlled conditions
Main function: protecting food from food spoilage
benefits for consumers: lighter(necessary for backpacking trips, cheaper shipping, convenience)
can be used in dehydrated state or reconstituted(water added-ex. Mashed potatoes)

4. Role of water activity (aw)
What is it?
Measure of free water available to support biological and chemical reactions
Dehydration lowers the water activity
Pure Water
1.0
Microorganisms
.085 to 1.0 to grow
Microbes stop growing
.7 to .85

5. Factors that affect quality of dried foods
Surface Area
Airflow
Temperature and Case Hardening
Oxidation

6. Surface Area
Greater the area, faster heat will travel to the center of food
Usually cut into smaller uniform pieces
If food is thick:
1. outside surface becomes damaged (unpleasant flavor changes)
2. incomplete dehydration (mold could grow)

7. Airflow
Helps keep moisture away as it is released from food – allows more rapid dry time and dry evenly
Home Food Dehydrator

8. Temperature and case hardening
For every 15 degree Celsius rise in temp, amount of moisture the air can hold in vapor form doubles
Faster the food is dehydrated, less change in food quality
If it is too fast, case hardening will occur making a dry skin around the food leaving moisture inside
more common in foods with dissolved sugars or salts (beef jerky or dried fruit)

9. Oxidation
Enzymatic browning occurs in foods high in polyphenols like apples, grapes, and tea
Many foods are pretreated to inactivate the enzymes and prevent browning

10. Controlling enzymatic activity
Heat Treatment: pasteurization (animal based products-milk/eggs), blanching (vegetables)
Sulfuring: fruits exposed to fumes from burning sulfur, sulfur combines with oxygen  sulfur dioxide
Advantage: shortened dry time, repels insects, fumes inhibit mold growth
Sulfiting: food soaked in sodium bisulfite solution, drained, and dehydrated
Disadvantages: increased drying time by 15-20%, food allergies to chemical
Both: heat sensitive nutrients (vit C) not affected, food retains original color

11. Dehydration methods
Tray Drying : easiest to use and most cost effective
enclosed cabinet that has trays of food
Fan pulls air into cabinet over heating coils
Air passes through screens to filter insects and dirt
Used in small scale drying for fruits & veggies

12. Dehydration methods
Belt Drying: grains, peas, and beans

13. Dehydration methods
Drum Drying: mashed potatoes, mashed sweet potatoes, tomato pastes
steam heats drums from inside to about 150 Celsius
Food picked up by rotating drum, dried, and scraped off by a blade into a collection system
Dried in less than one minute

14. Dehydration methods Spray Drying: fastest method (only a few seconds)
Liquid and paste foods sprayed into the top of a heated tower to 200 Celsius
Drops dehydrate and fall to a collection system
Milk, eggs, protein powders, flavorings, instant coffee

15. Dehydration methods Vacuum Drying: highest quality product, costly
food placed on heated trays (platens)
Platens transfer heat to food through conduction
Platens located in a vacuum chamber, atmospheric pressure lowered, boiling point lowered
Results in minimum heat damage

16. Advantages of Freeze Dried Foods
Dehydration methods
Freeze Drying also called lypholization or dehydrofreezing (food temp and atmospheric pressure is lowered to the point that water will sublimate out of the food)
food is frozen, placed in a vacuum chamber heated slightly by microwaves
Advantages of Freeze Dried Foods
Fresher flavors
More original color- oxygen removed from environment
Faster rehydration – less damage to the surface
Thicker pieces are possible because case hardening is less likely

17. Home dried foods Room Drying/Sun Drying: least expensive, unreliable
food arranged on trays or laid out into warm dry room to dry
Oven Drying
Cover oven racks with Teflon-coated screening, food placed on racks at F, oven slightly open
Herbs can be dried in the microwave
Using Home Dehydrators
Electric heating coil with air vents

18. Rehydration
Some dehydrated foods need to have water added back into them

19. Concentration Removing part of the water from the foods
Examples, fruit juice concentrates, condensed milk, maple syrup, condensed soups
Benefits: more economical to ship, extends food’s shelf life
Problems: cooked flavors, color changes, formation of sugar crystals, cause proteins to denature, risk of foodborne illness

20. Methods of concentration
Open Kettle: oldest method, used to make apple butter & molasses
Heat Evaporation: food exposed to high temps for a short period, fresher flavor than open kettle
Vacuum Evaporation: further reduce damage to heat-sensitive foods; used for grape and tomato juices and evaporated milk
Filtration: small particles flow through the filters, isolates food sources for use in concentrated form

21. Intermediate-moisture foods
Honey, jams, jellies, fruitcakes, pepperoni, beef jerky, partially dried figs, dates, and fruit strips
Low water activity level extends shelf life
Additives may be needed to preserve the quality