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Fruit and vegetable drying


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GTZ-ITFSP Fruit and vegetable drying

Processing of tree crops products - a farmer trainer training manual 3

Drying of fruits and vegetables

Drying of agricultural products is the oldest and widely used preservation method. It involves reduction as

much water as possible from foods to arrest enzyme and microbial activities hence stopping deterioration.

Moisture left in the dried foods varies between 2-30% depending on the type of food. In tropical countries,solar dryers can be used to dry fresh produce when average relative humidity is below 50% during drying

period.

Drying lowers weights and volume of the product hence lowers costs in transportation and storage. How-

ever, drying allows some lowering in nutritional value of the product e.g. loss of vitamin C, and changes of

colour and appearance that might not be desirable.

General procedure

Fruits

Fruits like mangoes, pawpaws, guavas and bananas, can easily be dried. However, they should be harvested

at the right stage and ripeness. Hard ripe stage in mangoes, pawpaws and bananas gives best results. Avoid

overripe, under mature fruits in order to obtain good products. To prepare the fruits for drying, wash

them thoroughly with clean water. Scrubbing with a brush might be necessary like in case of mango fruit

with a lot of latex cover. The fruits are peeled if necessary and cut into smaller uniform pieces to ensure

faster drying. Stainless steel knives are recommended for peeling and cutting of the slices or pieces.

To avoid discoloration and excessive vitamin losses, treatment with anti-oxidants like citrus (lemon) juice is

done. Fruits like pineapples may require pre-cooking to soften fibrous tissue hence hasten drying. Drying

is done on trays, which should be made of wood, fabric, plastic or sisal material. This is because metal

materials may affect the drying product negatively e.g. copper destroys vitamin C, iron rusts, aluminiumdiscolours fruits and corrodes.

Most fruits have natural acids and sugars which are preservatives therefore moisture contents of about

20% i.e. leathery and springy dry (not brittle) is good for storage. This is however dependent on the fruit or

vegetable. After the correct stage of dryness is achieved the product should be removed from the dryer

parked, and stored in a dry, dark store.

Select firm ripe fruit

Wash the fruits in clean water

Peel and remove damaged and discolored parts

Slice/cut into thin uniform slices or cubes

Pre-treat with lemon juice or sugar solution

Spread on trays and load into the dryer

Control the temperature by opening the dryer door

Pack the dried product in moisture-proof packs

Store in a cool, dark, dry, well-ventilated place


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4 Processing of tree crops products- a farmer trainer training manual

Fruit and vegetable drying GTZ-ITFSP

Vegetables

Vegetables like tomatoes, kales, cowpeas leaves, cabbages and pumpkin leaves can be dried. Tender healthy

vegetables are selected for drying. To prepare the vegetables for drying, wash and remove old and damaged

parts and then chop/slice for better drying.

Blanching

A solution of water and salt is prepared (varying in strength

depending on products) and boiled. The vegetables for

drying are dipped into the hot boiled solution in a piece of

clean cloth (or basket). Kale, other hard leafy vegetables

and cabbages should be dipped in the hot boiling solution

for 3 minutes while spinach and soft leafy vegetables re-

quire only 2 minutes.

To avoid overcooking, boil the blanching water before dip-ping the vegetables. Dip the vegetables in cold water im-

mediately after removing them from the boiled solution

to prevent further cooking. After blanching the vegetables

are spread on trays and dried, then parked and stored in

dry, dark store.

Blanching is carried out to improve the quality by inactivating the enzymes, reducing the microorganisms,

softening the vegetables, and preserve the natural colour of the green vegetables when they are dried.4

NB: Some vegetables like garlic, coriander (dhania) and parsley should not be blanched.

This is a rectangular shaped box

dryer with two chambers i.e.

heating chamber and a drying

chamber. It has been used at

farm-household level to dry

green vegetables with success.

The dryer can be easily carried

from place to place. The heating

chamber has a clear polythene

top while the drying chamber has

a black polythene top. Airflow is

free through the heating cham-

ber to the drying chamber.

Drying equipment

Portable indirect solar dryer


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Processing of tree crops products- a farmer trainer training manual 5

Improved Indirect solar Dryer

Also a rectangular shaped box dryer with two chamber

for heating and drying respectively. The two chambers

have clear glass tops. The dryer is also painted black for

better heat absorption.

The drying chamber has movable trays that can be re-

moved, loaded on to the chamber and shifted during

drying. The shifting of trays ensures even drying. Over

heating during drying is controlled by increasing ventila-

tion by opening the rear window of the dryer.

For better drying the dryer is rotated on its stand to face

the direction of the sun.

Required equipment include:

Kitchen scale-for weighing the fresh raw materials and dried product.

Squeezer (plastic)-for squeezing out lemon juice if necessary.

Measuring cups

Impulse heat sealer-To seal the product packaged in polythene bags

Sieve

Water buckets/pails/basins-for the washings.

Working tables and benches

Stainless steel knives

Packaging materials e.g. polythene bags (gauge 300)

Absorbent paper bags (for products like tomatoes)

Black plastic barrels to pack the sealed labelled product.


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6 Processing of tree crops products- a farmer trainer training manual


Selected recipes on drying

Dried mangoes slices

Ingredients:

Mangoes Lemon juice

Water

Method

1. Select and weigh hard ripe fresh mangoes.

2. Wash the fruits thoroughly in clean water.

3. Peel the mangoes

4. Slice the peeled fruits into thin uniform slices.

5. Prepare lemon juice/water solution in the ratio of 1:20.

6. Deep the mango slices in this solution then arrange them on the trays (single layer).

7. Load the trays in the dryer (the dryer should be facing the sun).8. Shift the trays in the dryer occasionally until the slices are dry.

9. Unload the dryer for sorting and packaging of the dried slices.

10. Pack the dried slices into moisture proof containers and store in a cool, dark place.

Dried bananas

Ingredients

Hard ripe bananas.

Lemon juice

Water

Method

1. Peel the bananas.

2. Cut thin longitudinal slices.

3. Dip the slices in the diluted lemon juice (I part lemon juice: 20 parts water). This step can be avoided if

product is meant for young children.

4. Arrange the slices in single layer on the trays.

5. Load the trays into the dryer

6. Shift the trays occasionally until the slices are dry.

7. Unload the dryer

8. Pack the dried bananas into moisture proof containers and store in a cool, dark place.


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Processing of tree crops products- a farmer trainer training manual 7

Dried tomatoes

Ingredients

Tomatoes

Salt.

Water

Method

1. Wash the ripe tomatoes after sorting and weighing.

2. Cut the fruits into quarters or halves and remove the seed.

3. Spread the pieces on the trays.

4. Sprinkle salt on the pieces ensuring all parts are covered (the pieces can also be dipped in salt solution,

20g of salt in 1 litre of water for at least 2 hours)

5. Dry the tomatoes in the dryer or without the dryer.

6. After 6 hours of drying the pieces start coiling.

7. Keep on opening them up anytime they coil.

8. The tomatoes will dry in 2-3 days.9. Unload the dryer, weigh and pack in brown absorbent papers ready for marketing.

Note:

While drying outside the dryer, the environment should be dust free and away from any contamination.

Wash the tamotoes Cut into half/quarter and remove seeds


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Dried pawpaw slices

Ingredients

Pawpaws

Lemon juice

Sugar

Water

Method

1. Clean firm ripe pawpaws thoroughly in two changes of water.

2. Cut fruit into quarters, vertically and horizontally.

3. Peel and trim off all defective parts.

4. Remove all the pips and thread.

5. Cut into 2-3 mm thick slices of uniform shape.

6. Meanwhile, prepare syrup by dissolving while stirring on gentle heat 2 parts of sugar for every part of

50% lemon juice (i.e. lemon juice diluted with water in the ratio of one to one).

7. After removing the syrup from the fire continue stirring until it cools.

8. Immediately after cutting, dip slices in syrup and hold for about 15 minutes.9. Remove the slices and drain off adhering syrup.

10. Spread slices carefully on clean trays in single layers and dry in the solar dryer until dry.

11. Unload the dryer and pack the dried slices in moisture proof black containers.

12. Store in a cool, clean, dark store.

Spread the tomatoes on the drying

trays and sprinkle salt on them

Pack dry tomatoes in brown paper

bags (not plastic bags!)


8 Processing of tree crops products - a farmer trainer training manual


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Wash the pawpaws Peel and slice the fruits

Scoop out all the seeds

Slice the pieces further for drying

Make sugar/lemon/water syrup

Dip the slices in the syrup before drying them

Weigh the dried slices and pack them in containers




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Dried guava slices

Ingredients

Ripe guavas

Sugar

Lemon juice Water

Method

1. Peel the fruits and chop into rings or required shapes.

2. Remove the seeds.

3. Prepare sugar syrup as for dried pawpaws.

4. Dip the guava slices in sugar syrup as for pawpaws and dry.

Dried avocado slices

Ingredients

Avocadoes

Method

1. Select mature but not ripe avocadoes (those that can ripen in 2-5 days)

2. Peel the avocado and remove seed.

3. Cut into 1cm square pieces of 2-3mm thickness. This is necessary for quick drying and to end up with

dried pieces that can fit in an oil press.

4. Arrange the pieces on trays and put in a solar drier until dry.

5. Remove the dried pieces and pack in airtight containers until ready for use.

NB: Dried avocadoes contain mainly oil and are used for oil extraction. The darkening caused by oxidation

has no effect on quality of oil. The dried product can also be pounded and added to porridge and other

foods to improve nutritional value.

Dried leafy vegetables

18Ingredients

Kale/cowpea leaves/cabbages etc.

Water

Salt

Method

1. Select and wash the vegetables thoroughly in clean water

2. Chop the vegetables (finely chopped vegetables dry faster but may, loose more vitamins).

3. Meanwhile prepare blanching solution (1part salt for 5 parts of water).

4. Blanch for 3 minutes.

5. Drain the vegetables well.

6. Dip the vegetables in cold water to avoid overcooking.

7. Spread on tray of the dryer in thin layers.

8. Load the dryer and dry till crispy dry.

9. Unload the dryer.

10. Pack in clean, moisture proof containers and store in dark, dry store.


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Dried onions20

Ingredients

Onions (bulb)

Method

1. Remove tops, roots and outer integuments of the onions

2. Wash thoroughly and carefully.

3. Slice the onions into thin slices (3 mm thick)

4. Spread evenly on the trays of a drier.

5. Dry to 5% moisture content (Ratio of prepared raw materials to dried product is 9:1).

6. Unload the dryers.

7. Pack and store.

Note:

No blanching is required

No preservatives added.

A drier used for drying onions can be selected and kept for onions only.

Fruit leathers

Made from dried fruit pulp (virtually all fruits and berries can be used).

Two or more fruits can be blended together into pulp before drying to give a highly flavoured and

sweet product.

Fruits with high water content like pawpaws and pineapples are best when mixed with ripe bananas.

For variation, chopped nuts can be added before fruit pulp is dried.

Fruit leathers are delicious and nutritious snacks.22

Ingredients Pawpaws

Mangoes

Nuts

23Method

1. Wash, peel and chop the fruits.

2. Chop the nuts

3. Mash the fruits and add the chopped nuts.

4. Pour onto a clean polythene sheet spread on a dryer tray.

5. Dry in the dryer until the pulp is rubbery and pliable in texture.

6. Roll up the leather with the polythene sheet, seal edges and store in airtight containers.


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Wash and peel the fruits and chop the nuts Mash the fruits and mix with chopped the nuts

Pour the mixture onto a polythene surface and

spread it out to dryRoll up the leather in the polythene

sheet

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