Dehydration & concentration - PowerPoint Presentation

Slide1

Dehydration & concentration

Anna Kitchen

Shannon Hawkins

Morgan

ModanySlide2

Three categories of processed foodsSlide3

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) Slide4

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 .85Slide5

Factors that affect quality of dried foods

Surface Area

Airflow

Temperature and Case Hardening

Oxidation Slide6

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)Slide7

Airflow

Helps keep moisture away as it is released from food – allows more rapid dry time and dry evenly

Home Food Dehydrator Slide8

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) Slide9

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 Slide10

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 Slide11

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 Slide12

Dehydration methods

Belt Drying: grains, peas, and beans Slide13

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 Slide14

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 Slide15

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 Slide16

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 Slide17

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 140-150 F, oven slightly open

Herbs can be dried in the microwave

Using Home Dehydrators

Electric heating coil with air vents Slide18

Rehydration

Some dehydrated foods need to have water added back into themSlide19

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 Slide20

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 Slide21

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