Dehydration & concentration Anna Kitchen Shannon Hawkins Morgan Modany

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

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)

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

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

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)

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

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)

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

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

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

Dehydration methods Belt Drying: grains, peas, and beans

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

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

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

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

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

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

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

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

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