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Original:Solar and Energy Conserving Food Technologies 10
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- (Peace Corps, 1984, 175 p.)
The use of solar food dryers
OVERVIEW AND GOALS:
Although the dehydration process is not complex, it does require following certain guidelines to ensure a dried product of high quality. In this session, the participants begin to put the guidelines into practice.
To learn how to prepare foods for drying
To learn how to operate the Solar Food Dryer during the drying process
To learn how to test foods for drying
Putting Food By, Chapters 2 and 21.
Improved Food Drying and Storage Manual, Session A-3.
Preparing Food for Drying, Handout 8A Use of the Dryers, Handout 8B Tests for Dryness, Handout 8C Pre-Drying Treatment of Foods, Handout 8D Post-Drying Treatment of Foods, Handout 8E
Model Solar Food Dryer 5-10
Cutting hoards 10-20
Variety of fruits and vegetables, meat, fish and herbs (both fresh and dried) Lemons
5-10 Small plates
Medium-sized cooking pot
Gauze cloth for blanching
Small tin can
Cardboard box for sulfuring
Prepare a tray, using a variety of foods, in such a way as to show both several right and wrong ways to load a tray for drying.
Prepare enough plates for a variety of dry food samples to have one for every 3-4 people in the group.
PROCEDURES AND ACTIVITIES:
1. (15 minutes) Introduction
Review session objectives.
Briefly discuss the importance of drying food correctly. Stress the fact that it is a relatively simple process that should generally follow the guidelines to be discussed in this session.
Discuss the necessity for each person to experiment with their dryer both during and after the course using a variety of foods under different climatic conditions, to determine what works best according to their needs and situation.
Display the incorrectly prepared drying tray to the group. Ask what people think has been done correctly and incorrectly in loading the tray, and why. Ask the group what changes they think necessary for correct loading of the tray, and discuss the reasons for making the changes.
Don't suggest any necessary corrections the group did not mention, as there will be an opportunity to do so at the end of the session on the basis of information gained.
2. (30 minutes) Solar Food Drying Guidelines
Distribute and review "Preparing Food for Drying", Handout 8A, "Pre-Drying Treatment of Foods", Handout 8D, and "Use of the Dryers, 8B questioning the participants wherever appropriate as to the importance of doing particular steps. Demonstrate the steps whenever possible as they are being discussed.
It may be helpful to have the guidelines written on newsprint and displayed so that people can easily follow the points made during the demonstration without having to refer to their handouts.
3. (30 minutes) Tests for Dryness
Give a prepared plate of dried foods to every 3-4 persons in the group. These may be used for practicing tests for dryness as each one is discussed.
Ask the participants what tests for dryness they are familiar with, either used locally or from their own experience. Record these on flipchart paper and discuss the effectiveness of each method.
Distribute and review "Tests for Dryness," Handout SC, and "PostDrying Steps", Handout BE.
Use the same procedure of demonstration and ongoing questioning during the discussion as was used in Step #Z.
4. (15 minutes) Summary
Again, present the tray of food used in the beginning of the session, and ask the participants if there are any additional corrections they think should be made in the loading of the tray, (i.e., to separate foods requiring the same temperature range for drying).
5. (30 minutes) Loading Dryers
Re-emphasize the importance of ongoing experimentation and practice with the drying process. If weather permits, have people form the same construction groups as they did the previous day to load their cardboard model dryers and correctly orient them in the sun. If the weather is cloudy, postpone this activity until the first clear morning.
It is suggested that participants gain experience with one load of food before using any of the pre treatment methods.
All materials and food for loading the dryers, including those materials that will be used in pre-treatment methods, should be made available for people to use on their own as needed throughout the course. At this point tell the participants where supplies will be kept.
Circulate among the groups to offer guidance. Occasionally ask why they are doing a particular step to make sure that they understand the principles involved.
Inform each group that they are responsible for the drying process and care for their dryer from this point on (i.e., operating the vents, bringing dryers in in case of rain, etc.).
Encourage participants to share with the group on an ongoing basis both their "successes" and "failures" in drying food. This may be done during the time set aside for presentations either at the end or beginning of each day throughout the course.
PREPARING FOOD FOR DRYING
1. Clean the trays and drying chamber as needed between use.
2. Select produce that is firm and ripe. Over ripe food will result in a dried product of low quality.
3. Use fresh, lean meat and fish.
4. Wash food well. Dry immediately.
5. Peel and remove seeds from fruits and vegetables if necessary. Try to avoid peeling whenever possible as that causes vitamin loss.
6. Slice fruits and vegetables less than 1 cm. thick, or grate them to the thickness desired.
7. Cut fish in half, filet, or cut into long thin strips.
8. Slice meat 1 cm. thick, or cut into long, thin strips.
9. Pre-treat foods if desired (see Handout: "Pre-Drying Treatment of Foods")
10. Puree fruit and vegetables to make leather. Season to taste. Pour onto a metal tray that has been lightly oiled or lined with food-grade plastic.
USE OF THE DRYERS
1. Load dryers evenly.
2. Don't overlap food. Leave sufficient space for air to pass between pieces.
3. Dry strong-smelling foods separately.
4. Dry foods together that require the same temperature range.
FRUITS AND VEGETABLES: 38-60ÂºC
MEAT AND FISH: 60-66ÂºC
5. Load dryers early in the morning and only on clear days.
6. Use the indirect method to avoid cooking meat and fish. Use whenever possible with herbs to avoid loss of flavor, and with fruits and vegetables to prevent loss of vitamins that are sensitive to light.
7. Turn foods as needed during the drying process.
8. Rotate trays within the dryer if necessary for a more even drying rate.
9. Operate vent doors to control temperature curing the day. Close them in the evening to prevent dehydration from the night air.
10. Use a thermometer to maintain the desired temperature range until familiar with the performance of your dryer.
11. Allow food to cool before closing vent doors or testing for dryness.
12. Keep an eye on the food as it dries. Leaving it in too long will cause scorching and unnecessary vitamin loss.
13. Foods will take from 1/2 to 3 days to dry. (Original moisture content of the food, humidity of the air, amount of sunshine, and temperature and air flow inside the dryer will all effect the rate of dehydration.)
TESTS FOR DRYNESS
FRUITS ARE CONSIDERED DEHYDRATED WITH APPROXIMATELY 20% MOISTURE CONTENT, AND VEGETABLES WITH 10-15%.
THE FOLLOWING TEST SHOULD BE USED TO DETERMINE WHEN FRUITS, VEGETABLES, MEAT, FISH AND HERBS ARE READY FOR STORAGE.
FRUITS AND MEAT:
A handful of fruit or meat when compressed should neither stick together nor leave any trace of moisture in one's hand.
It should feel leathery and flexible.
Meat may be further dried to the point where it feels fairly stiff.
Should feel flexible and leathery, but generally drier than fruits. Some vegetables will feel almost brittle. Pieces should fall apart after being squeezed together.
Should retain no imprint when squeezed between the thumb and forefinger. Will feel either leathery or brittle.
Crumble easily when rubbed together.
PRE-DRYING TREATMENT OF FOODS
Pre-treatment of foods for drying is optional, but may he done to reduce loss of color, flavor and certain vitamins. The following four treatments are the ones most commonly used.
BLANCHING: (used for vegetables) Helps retain color, flavor, and possibly some vitamin A, C and S.
1. Prepare food for drying.
2. To blanch vegetables, place them loosely in a basket, strainer or gauze bag.
3. Suspend either in boiling (salted) water or in steam, for the required time (see notes below) until almost cooked. Dip into clean cold potable water to cool, then drain thoroughly.
- Blanching may also be carried out be stirring the prepared vegetables into a container of boiling water, replacing the lid and leaving for the recommended time. Lift out with a skimmer and re-use the water for additional batches of the same vegetable.
- Mushrooms, onions, peppers, parsley and other herbs are not blanched before drying.
- Examples of recommended approximate blanching times for typical vegetables:
Green leafy vegetables and sliced beans
2 - 2 1/2
2 1/2 - 3
1 1/2 - 2
3 - 3 1/2
4 - 5
3 - 4
6 - 8
5 - 6
LEMON DIP: (used for fruits and vegetables) Helps prevent darkening; increases the Vitamin C content.
Squeeze lemon juice directly onto the prepared foods, or soak them for 5-10 minutes in a solution of 1 tablespoon of lemon juice to 1 cup of water.
SULFURING: (used for fruits)
Helps prevent browning and loss of vitamins A and C. Caution: There is some controversy about the health aspects of ingesting sulfured foods, and great care must be taken not to inhale the sulfur dioxide fumes as they can cause damage to lung tissue.
1. Stack prepared trays of food outside on the ground. Leave a space of 5-10 cm. between trays.
2. Place a small tin of sulfur (use 2 table spoons of sublimed sulfur per kilo of food. Available at pharmacies.) on the ground, 2D cm. in front of the trays.
3. Light the sulfur, and cover immediately with a sufficiently large cardboard box. (The box should have a small lower opening cut in front of the burning sulfur end en upper Opening cut on the opposite side for ventilation).
4. When the sulfur has burned completely, close the two openings and begin to time the sulfuring process.
5. Leave small pieces of fruit in for 20-30 minutes. Larger pieces may be sulfured for up to an hour. (Consult "Putting Food By", Chapter 21, for more specific times.)
6. Lift the box off, pointing it away from you.
7. Place the trays of food into your Solar Food Dryer and dry as usual.
SALTING OR BRINING: (used for meat and fish)
Both salting and brining facilitate the drying process, as the salt helps to draw cut moisture as well as inhibit the growth of microorganisms.
1. Coat prepared pieces of fish liberally with pure pickling salt, using about 1 kilo of slat per 2 kilos of fish or meat.
2. Stack pieces fleshside up on a slatted wooden rack outdoors. Don't stack more than 12 layers deep.
3. Leave for 1-2 weeks.
4. Add weights on top of the pile to compress it as the brine is formed.
5. Wash fish to remove salt.
6. Wipe dry, and place in the Solar Food Dryer.
1. Prepare a brine of 2 1/2 cups of pickling salt for 3 liters of water.
2. Soak strips of meat or fish for 1 or 2 days.
3. Remove and wipe dry.
4. Place in the Solar Food Dryer for drying as usual.
POST-DRYING TREATMENTS PASTEURIZING AND CONDITIONING
Both these steps are optional, precautionary steps which may be done to reduce the chances of dried foods spoiling during storage.
Food can be pasteurized after drying to kill any insect eggs and larvae that may still be present. To do this either keep the food at 57ÂºC for an hour, or 80ÂºC for 10 - 15 minutes.
Note: Use of an oven may be necessary to achieve the desired temperatures if they cannot be reached using the Solar Food Dryer.
When drying is completed, some pieces will be more moist than others because of the size of the pieces or their location in the dryer. Conditioning is a process used to distribute the residual moisture evenly in the fruit and reduce the chance of spoilage.
After the dried food has cooled, loosely pack it in plastic or glass containers to about 2/3 full. Metal containers should be lined with paper first, as they may give an unpleasant flavor to the food. Cover the containers tightly and let them stand for 2 to 4 days.
Shake the containers daily to separate the pieces and check for signs of condensation on the lids. If condensation occurs, the fruit should be returned to the drying trays for more drying.