1. DRYING
Introduction
Foods - spoiled by food microorganisms or through enzymatic reactions
. Bacteria, yeast, and molds need sufficient amount of moisture to grow and cause spoilage.
Reducing the moisture content of food prevents the growth of these spoilage-causing microorganisms and slows down enzymatic reactions
Drying (dehydrating) food - the oldest and easiest methods of food preservation.
Dehydration - the process of removing water or moisture from a food product.
Easy to carry- ideal for backpacking, hiking, and camping
A way of preserving seasonal food.

2. Drying Techniques Sun or solar drying Freeze drying Drum drying
Spray drying
Foam mat and vacuum belt
Convection air & Superheated steam (tray, tunnel)
Osmotic drying
Microwave

3. Drying Techniques (continued)
Combination of different techniques
Vacuum- osmotic
Osmotic – microwave
Ultrasound pre-treatment followed by drying
Fluidized bed
Pulse combustion

4. Drying Rates

5. The basics of food dehydration
Three things are needed to successfully dry food
Heat — hot enough to force out moisture (140°F), but not hot enough to cook the food;
Dry air — to absorb the released moisture;
Air movement — to carry the moisture away.
Foods can be dried using three methods:
In the sun— requires warm days of 85°F or higher, low humidity, and insect control;  recommended for dehydrating fruits only;
In the oven;
Using a food dehydrator — electric dehydrators take less time to dry foods and are more cost efficient than an oven.

6. TYPES OF FOOD TO DRY
Many kinds of fresh fruits, vegetables, herbs, meat, and fish can be dried.
Fruits are easier to dry than vegetables
Vegetables that are also practical to dry include peas, corn, peppers, zucchini, okra, onions, and green beans.
Fresh herbs of all types are suitable for drying.
Lean meats such as beef, lamb,
Lettuce, melons, and cucumbers are a few foods that do not dry well.
Microwave Radiation
can be used for drying herbs. Although this process actually cooks the herbs, the end product is just about the same.

7. Most vegetables and some fruits should undergo a pretreatment, such as blanching or dipping.
Blanching is briefly precooking food in boiling water or steam, and it is used to stop enzymatic reactions within the foods. Blanching also shortens drying time and kills many spoilage organisms.
Fruits may be dipped in ascorbic acid or citric acid in place of blanching.
steam blanching for fruit and vegetables, water blanching (vegetables only), syrup blanching (fruits only).
Dipping is a pretreatment used to prevent fruits such as apples, bananas, peaches, and pears from turning brown. Ascorbic acid, fruit juices high in vitamin C (lemon, orange, pineapple, grape, etc.)
Sulfuring
Sulfuring is the best antioxidant treatment for preserving color. Sulfur also helps prevent loss of vitamins A and C. Sulfur is not a preservative in itself, but it discourages insects and microbes, which can cause spoilage.

8. Pre-treatment
Some fruits need to have their enzymes inactivated before drying, especially those that oxidize when exposed to air (e.g. bananas, apples, pears)
Ascorbic Acid
Fruit juice dip
Honey dip
Syrup blanching
Commercial acids

9. Natural sun drying
Sun drying is recommended for drying fruit only. Sun drying is not recommended in cloudy or humid weather. The temperature should reach 85°F by noon, and the humidity should be less than 60 percent. Outdoor dehydration can be difficult in high humid area. All food that is dried outdoors must be pasteurized.
Drying with a food dehydrator or Oven drying
Dehydrate at 140°F. Check food often and turn pieces every few hours to dry more evenly.
Spread the food in a single layer on racks or cookie sheets. Check food often and turn pieces every few hours to dry more evenly.
Drying time will vary

10. There are two methods of sulfuring using (1) sulfur fumes or (2) a sulfite solution.
popular are thyme, tarragon, rosemary, mint, sage, sweet basil, bay leaf, parsley, marjoram, savory, oregano, chervil, chives, and dill and they give off a soft, pleasant fragrance. Young, tender leaves are more flavorful and aromatic than older leaves.

11. Tunnel Dryer
Tray Dryer

12. Hot Air Drying
Carrots
Blueberries

13. Vacuum Belt Drying Of Blueberries

14. Solar Tray Dryer

15. SPRAY DRYING

16. PREPARING THE MEAT
Any lean meat can be dried. Beef is especially good; fish and poultry dry well. Be sure to use fresh, lean meat and cut off all fat and connective tissue. Fat becomes rancid easily and will spoil the dried meat.
Partly freezing the meat before cutting makes it easy to slice.
Smoke Drying
Starting temperature should be 80 degrees F. (27 C.), then it should be increased gradually to 120 F. (49 C.). Smoke the desired texture (24 to 48 hours).
Use any hardwood such as hickory or oak for smoking the drippings should be collected or it will burn and produce smoke that gives the meat an unpleasant flavor.
Osmotic Dehydration
can be used for partial drying. Osmotic dehydration is the phenomenon of removal of water from lower concentration of solute to higher concentration through semi permeable membrane results in the equilibrium condition in both sides of membrane. Osmotic dehydration found wide application in the preservation of food-materials since it lowers the water activity of fruits and vegetables. Osmotic dehydration is preferred over other methods due to their color, aroma, nutritional constituents and flavor compound retention value.

17. In osmotic dehydration the solutes used are generally sugar syrup with fruit slices or cubes and salt (sodium chloride) or brine with vegetables.
multicomponent diffusion process. In this process water flow from fruits or vegetables to solution and along with water some components of fruits and vegetables such as minerals, vitamins, fruit acids etc. also move towards solution.
The sugar and salt migrate towards the fruits and vegetables. The process of complete osmotic dehydration has been shown by flow diagram.
The most important products of commercial importance available in market made from fruits are murabbas of gooseberry (Aonla), apple, candies of different fruits and vegetables like pethas, sweets of parwal made by osmosis in sugar syrup.
In pickles making from raw mango it is treated in brine solution before drying. Various vegetables are treated in brine to reduce their moisture content.

18. Fruit Leathers Made from pureed fruit
Can use fresh/frozen fruit or canned fruit
May add sugar, honey, or lemon juice for flavor and color retention
May add coconut or nuts
Dry on special drying tray that comes with
dehydrator
Dry until pliable; no wet spots; not crispy