AY Honors/Food - Drying/Answer Key

1. List at least three different ways to dry foods.

Sun Drying

Food can be dried in the sun, but only if the temperatures are near 100°F (38°C) and the humidity is low. The fruit must be covered with cheesecloth (or something similar) to protect it from insects. If it is dried on a table, the table legs should be set in cans of water to prevent insects from crawling up the legs and getting into the fruit. The fruit will take several days to dry, and the humidity and other weather conditions must be monitored. If the temperature drops significantly during the night, dew may form, and the fruit will absorb it quickly. Because of this, it may be necessary to take the fruit indoors at night.

Oven Drying

This is the fastest way to dry food, but only small quantities at a time can be dried this way. The oven is preheated to about 140°F (60°C) and the food is placed on racks in the oven. The door must be held open about two inches (5cm) for a gas oven, or about 4 inches (10cm) for an electric oven. A thermometer is placed in the center of the rack to make sure the temperature stays near 140°F (60°C). A fan should be placed near the open oven door so that air inside the oven can circulate and allow the moisture to escape.

The food trays must be rotated every 30 minutes because the heat inside the oven will not be distributed evenly. Rotate the trays from front to back, top to bottom, and left to right.

Food Dryer

Food dryers can be purchased or home-built. They can dry more food than an oven but it takes a little longer. They also use less electricity than an electric oven. A food dryer is an enclosed box with a heat source, a fan, and a set of racks upon which the food is placed. Most home-built food dryers use a 100 watt light bulb as the heat source. It takes four to six hours to dry a batch of food in a food dryer, and like ovens, they operate at about 140°F (60°C).

You can build your own food dryer by lining a cardboard box with Styrofoam insulation, and then covering the Styrofoam with aluminum foil. Alternately, you can use insulation board with the foil already attached (this is available at most home improvement stores). It is very important that you line the insulation with foil, as this reflects the heat away from the insulation which would otherwise melt. Make an insulated lid for the box as well, but leave a gap at one end for moisture to escape.

The next thing you will need is a light fixture. Use a simple porcelain base, and mount it to a steel ceiling box (both of these are available in the electrical section of a hardware store). If desired, you can also use the thermostat from a water heater to control the temperature. These thermostats are generally settable between 40°C- 65°C - you will want to set it to 60°C. If you buy a deep ceiling box, you can mount the thermostat inside it, but make sure it makes good contact with the ceiling box so that heat is conducted to it. If you cannot mount the thermostat inside the box you will need to cover the terminals, as they will both carry household voltage (which is enough to kill a person who comes in contact with it).

The last item you will need is an extension cord. Cut the "female" end of it off and throw it away. Make a hole in box and poke the cut end through. Then run it through an opening in the ceiling box. Strip the ends of the wire and connect them to the porcelain light fixture. Tighten the clamp on the ceiling box to hold the extension cord in place. Screw in a 100 Watt bulb and plug in the cord. If the light does not turn on, unplug and check your wiring.

If you opt to use a thermostat, wire the "hot" wire on the extension cord (this is the one that connects to the narrower of the two blades on the plug) to either terminal of the thermostat. Run a wire from the remaining terminal of the thermostat to the light fixture. The neutral wire (connected to the wide blade of the plug) should be connected to the remaining terminal on the light fixture.

Finally, mount the fixture inside the insulated box and rig up a rack to hold your food trays. Keep a close eye on it the first time you use it.

If you do not use a thermostat, place a thermometer inside the box and keep an eye on it. You can control the temperature by varying the width of the gap in the lid, or by using a different wattage light bulb.

Freeze Dry

You can't do this at home, but if food is frozen then placed in a vacuum chamber and heat is applied you can freeze dry the food. In freeze drying the water in the food goes directly from solid to vapour state without passing through the liquid state. This allows the water to escape without doing as much damage to the cell structure of the food. The result is a food that looks less shrunken and tastes more like fresh.

Spray Dry

A spray dryer takes a liquid stream and separates the solute or suspension as a solid and the solvent into a vapor. The solid is usually collected in a drum or cyclone. The liquid input stream is sprayed through a nozzle into a hot vapor stream and vaporised. Solids form as moisture quickly leaves the droplets. A nozzle is usually used to make the droplets as small as possible, maximising heat transfer and the rate of water vaporisation. Droplet sizes can range from 20 to 180 μm depending on the nozzle.

Spray dryers can dry a product very quickly compared to other methods of drying. They also turn a solution, or slurry into a dried powder in a single step, which can be advantageous for profit maximization and process simplification. Powdered milk, tea and coffee are common product that are spray dried.

Drum Drying

Drum drying is a method used for drying out liquids; for example, milk is applied as a thin film to the surface of a heated drum, and the dried milk solids are then scraped off with a knife. Powdered milk made by drum drying tends to have a cooked flavor, due to caramelization caused by greater heat exposure.

Compared to spray drying, drum drying is a more intense heat treatment which results in more denatured proteins. The powder is less soluble as a result. The temperature uniformity of the heated roller/drum is poor so spray drying results in better quality milk powder.

Other products where drum drying may be used: starches, breakfast cereals, baby food, and instant mashed potatoes.

2. Why and how do you sulphur fruits?

Commercially prepared dried fruit may contain sulfur dioxide which can trigger asthma in sensitive individuals, though dried fruit without sulfur dioxide is also available, particularly in health stores. The sulphur is added to "fix" the colour of the product. "Organic" dried fruit is produced without sulphur which results in dark fruit and the flavor is much more characteristic of the fresh fruit. The color of some fruits can also be "fixed" to some extent, with minimal impact on flavor, by treating the freshly cut fruit with a preparation rich in Vitamin C (e.g., a mixture of water and lemon juice) for a few minutes prior to drying.

Sulphuring fruit is accomplished by burning a block of sulphur in an enclosed box (such as a dehydrator) with the fruit inside. The burning sulphur gives off sulphur dioxide which fixes the color of the fruit. This should only be done outside.

3. How is dried fruit stored and protected from insects?

As soon as it cools, dried fruit should be packed into insect-proof containers, such as glass jars or metal cans with tight-fitting lids. Do not let sulphured fruit touch metal, as this will cause the fruit to become discolored. You can pack fruit into plastic bags and then place that in a metal container. Plastic bags are not 100% insect (or rodent) proof, so make sure you store the fruit in a place where they cannot get to it. A cool, dry place is best.

4. How are dried foods reconstituted?

Just add water. You can also simmer them in boiling water for 15 minutes.

5. What is important in selecting fruit to be used in making fruit leather?

The fruit must be ripe, or slightly overripe. Be sure to use good quality fruit, as it will make good quality fruit leather. Select fruit that is fresh, and fully sound - basically, the same things you look for when selecting fruit for the table. Cut out any bad parts of the fruit. The saying, "one bad apple spoils the whole lot" applies to fruit leather, as a bad piece of fruit can impart a bad flavor to any of the fruit it comes into contact with. In making fruit leather, the fruit is pureed before drying, so the bad fruit will come into contact with all the fruit.

6. How are dried nuts stored?

Dried nuts must be stored in a cool, dry place in air-tight containers to prevent reabsorption of moisture.

7. Dry the following and provide samples for testing:

a. Bread. Make crumbs and use in a recipe for sampling.

Bread can be dried without the use of special equipment by placing several slices in a large bowl and covering it with a towel. The bowl should be kept indoors. After several days, the bread will be dry (also known as "stale") and it can then be crumbled. The usual use for bread crumbs is to make stuffing. You may use any stuffing recipe you like (as long as it uses bread crumbs), or you can use this one:

Adventist Youth Honors Answer Book/Stuffing Recipe

b. Fruit leather

Wash the fruit and puree it in a food processor. Line a shallow pan with wax paper, being sure to bring the edges up so that the pureed fruit cannot run under it. Pour the fruit puree into the pan until it is about a quarter inch deep (0.6 cm). Place it in the food dryer set to 140°F (60°C). Check it after four hours (but it may take much longer). Remove the fruit when it is tacky to the touch. Remove it and the wax paper from the pan and slice into thin strips, leaving the wax paper attached. Roll the strips (and wax paper) into a spiral and place in a sealable plastic bag. Store in a cool dry place. Fruit leather can be stored for up to six months.

c. Vegetable leather

You can make vegetable leather from just about any type of vegetable so long as it is pureed first. A shortcut is to use baby food as the starting point, and then proceed as with fruit leather. Here are two other recipes (in case your Pathfinders rebel at the thought of eating baby food).

Pumpkin Leather

• 2 cups of canned pumpkin, or 2 cups of fresh pumpkin, cooked and pureed.
• 1/2 cup honey
• 1/2 teaspoon cinnamon
• 1/4 teaspoon nutmeg (powdered)
• 1/4 teaspoon cloves (powdered)

Combine ingredients and dry at 140°F (60°C) (same as for fruit leather).

Tomato Leather

Core and slice ripe tomatoes into quarters. Boil for 15 minutes. Remove from water, force through a colander or a sieve. Add salt (if desired for flavoring), and simmer until thick. Spread on a plastic or wax paper lined tray and dry at 140°F (60°C) (same as for fruit leather).

d. Fruit slices

Most fruits need to be pretreated before they are dried. Apples should be cored, peeled, and sliced. Fruits with pits (such as peaches, nectarines, and cherries) should be split in half and pitted.

Thin slices of fruit dry quicker than thick slices, so it is important to slice fruit into uniform thicknesses so that it dries evenly.

Fruit with thick, waxy skins (such as blueberries and cherries) must be cracked before it is dried. Cracking the skin allows the moisture to escape. To crack the fruit, drop it in boiling water for 30-60 seconds, and then quickly move it to very cold water.

Some fruits, such as apples, pears, and apricots become discolored quickly after they are peeled and sliced. To prevent them from turning brown, mix two teaspoons of ascorbic acid in one cup of water, and dip the fruit in this solution as you work with it. One cup of this solution should be enough to treat five quarts of fruit. Ascorbic acid (more commonly known as Vitamin C) is available in most drug stores. You can also crush a 500mg tablet of Vitamin C and mix that with a quart (one liter) of water. Soak the fruit in that solution for two to three minutes.

Once the fruit has been prepared, arrange it in a single layer on a drying tray with the cut side up (if cut in half). Finally, place the trays in a food dryer, and wait. The amount of time varies depending on the fruit, how thick the slices are, et cetera. It should take between four and ten hours to dry.

e. Vegetable slices (such as carrots) or pieces (such as peas)

Select ripe, high quality vegetables. Cut out any bad spots, discard overripe pieces, and slice into thin, uniform pieces (unless you are starting with small vegetables such as peas).

Nearly all vegetables need to be blanched before they are dried. Blanching stops enzymes from destroying the vegetables. Drying by itself does not stop the enzyme action. To blanch vegetables, drop them in boiling water for a minute or two. Then cool them in ice water for the same amount of time that they were blanched. Blanching does remove some nutrients from the vegetables, so be sure to blanch them for only the minimum specified time (see table).

Arrange the vegetables on a drying tray in a single layer. Place the trays in the dryer at 140°F (60°C) with a minimum of one inch between trays. Drying will take between four and twelve hours. Turn the vegetable pieces every thirty minutes and rearrange them on the tray so that they are dried evenly (different areas on the trays will dry at different rates). The pieces are dry when they are hard and brittle. You can test them by striking a piece with a hammer. If it shatters, the vegetable is dry.

Vegetable	Blanching Time (minutes)	Drying Time (hours)
Asparagus	3.5 - 4.5	1 - 3
Green Beans	3 - 4	2.5 - 4
Carrots	3.5	2.5 - 4
Corn	5 - 8	4
Onions	do not blanch	1 - 3
Peas	3	3
Potatoes	6 - 8	2 - 4
Summer Squash	1.5 - 2	2.5 - 3
Tomatoes (3/4" thick)	1	3.5 - 4

f. Vegetarian jerky

• 1 lb firm tofu
• 1/2 cup Bragg Liquid Aminos
• 3-4 tablespoons liquid smoke
• 1 teaspoon garlic powder
• 1 teaspoon salt
• 1 teaspoon pepper
• 1 teaspoon honey
• 1 teaspoon onion powder
• 1/8 cup water

1. Drain and slice the tofu into quarter-inch (5mm) thick, long, narrow slices
2. Mix all the ingredients, adding the tofu slice last in shallow baking dish. Cover and refrigerate overnight.
3. Dry at 140°F (60°C) 4-6 hours, turning hourly.

Easy Vegetarian Jerky

• Stripples (Worthington)

1. Spread Stripples out in a single layer in food dehydrator or oven (set on lowest temperature setting).
2. Turn stripples once or twice as needed for even drying, throughout drying time.

g. Parsley or some other herb

Fresh parsley, mint, oregano, basil, marjoram, and rosemary can be dried without any special equipment. Simply bundle the fresh herbs and hang them in a dry corner of the kitchen out of direct sunlight for a couple of weeks. You can also dry them by spreading them out on a dish towel.

8. Reconstitute a vegetable and cook for sampling.

Vegetables can be reconstituted by soaking them in water for two or three hours. They should return to their full size. Cook any way you like.

References

• http://extension.usu.edu/files/foodpubs/fn330.pdf Utah State Extension
• http://www.extension.uiuc.edu/~vista/html_pubs/DRYING/dryfood.html University of Illinois at Urbana-Champaign.
• http://www.thefarm.org/charities/i4at/surv/dryguide.htm
• http://homeorchard.ucdavis.edu/8005.pdf Storing nuts