Solar drying can take plarce directly in the sun with the produce spread out on pieces of plastic or on large concrete slabs. There are however disadvantages to this method - somebody has to stay at home throughout the drying period to chase Of domestic animals, to remove the produce when the weather becomes, too windy and dusty or when it rains. The dried product is often of quality as a result of grit and dirt. The product is often unhygienic as a resultof micro onganisms and insects such as flies.

The technology and capital required to dry fruit and vegetables by solar dryers is basic and the entire operation can be completed in most kitchens. The structure can be very basic e.g. a box frame covered with plastic sheeting. A basict box-type low cost solar dryer can be constructed at home or by a handyman. Typically it is made of wire-mesh trays in a wooden framework surrounded by a clear plastic sheet. The solar cabinet dryer type has a surface of 10m2 and is capable of drying 20 to 35 kg of fresh produce (depending on commodity) over a period of 3 to 4 days. Smaller portable models of the dryer can also be constructed. In South Africa there are manufactunsrs that can supply solar dryers or you can construct your own dryer since it is fairly easy to make. Sometimes, large solar dryers are used for commercial drying of fruit and fish. In larger solar dryers, fans or air pumps are used to circulate air in the dryer. Large dryers are most often specifically designed for the terrain, the produce to be dried and the volume of produce that must be processed.

There are a number of advantages to using a solar dryer:

1. Drying is faster beacause it is warmer inside the dryer than outside;
2. Less risk of spoilage because of the speed of drying (if the drying process is slow the fruit starts to ferment and the product is spoilt);
3. The product is protected against flies, pests, rain and dust;
4. It is labour saving;
5. The product can be left in the dryer overnight or during rain;
6. The quality of the product is better in terms of nutrients, hygiene and colour.

Cleanliness and hygiene are very important in the processing of dried fruit and vegetables. Raw contaminated by mould must not be used in processing - remember that the quality of fruit and vegetables cannot be improved by drying. Solar drying requires a number of pre-drying steps:

Selection of food to be dried

Only ripe and good quality fruit and vegetables should be selected to be dried. Each piece should be selected individually since one rotten or mouldy piece may spoil a whole batch.

Washing selected food

Work surfaces should be cleaned before handling fruit or vegetables. Water, treated with household bleach (add 400 ml bleach to 20 litres of water - a normal household bucket). One bucket of treated water is enough for 20kg of fruit. Selected fruit and vegetables should be washed and scrubbed individually in the treated water and care must be taken to avoid breaking the skin of the fruit during cleaning and thence contaminating the flesh.

Blanching and peeling

Before drying all, vegetables should be blanched in steam to halt the action of enzymes but the blanching of fruit is optional. When vegetables are blanched, they are not immersed in water but cooked through exposure to steam. Steam blanching is recommended because it prevents the loss of nutrients and stops pieces sticking together. It is important not to under blanch, because the enzymes will not be inactivated totally and the dried vegetables may spoil during storage.

Hygiene is also important when fruit or vegetables are peeled. Hands should be thoroughly washed and peeling knives and working surfaces should be cleaned in fresh bleach solution before use. Sharp knives must be used to avoid peeling the fruit too thickly and thereby wasting the product. Peelings and seeds should be disposed of as soon as possible because they attract flies and other insects it can be used as animal feed or as mulch or be buried if there is no other use.

Cutting and slicing

The thickness of the fruit pieces depends upon the kind of ruit being dried. A few handy hints:

1. Thicker slices will dry at a slower rate than thinner pieces;
2. Thicker pieces may not dry fully and may subsequently deteriorate after packing;
3. Very thin pieces tend to stick to the drying trays and will be difficult to remove.

Tray loading

Trays should be washed and cleaned to remove any fragments of dried fruit. It is better to start the loading process while the food is being sliced. This reduces the problem of sticking together in the bowls and will allow drying to start as soon as possible. The fruit should be placed close to each other on the trays without overlapping.

Dryer loading

The dryer should be placed in a level, sunny area, fully exposed to the sun thoughout the day. Before loading, the inside of the drying cabinet should be swept clean and then wiped out with a clean, damp cloth. The plastic covers outside should be brushed or washed clean of dust because dirty plastic will reduce dryer performance and increase drying times. The doors should be dosed immediately after each tray has been loaded and not left open until the next tray is fetched. During the first few hours of drying, particularly during very hot and sunny weather, fruit may dry at such a rate that moisture condenses on the inside of the plastic covers. This can be avoided by opening the loading doors slightly (20 mm) to improve air circulation. The gap should however be covered with mosquito mesh. Under fine and sunny conditions the fruit slices should be dry after 2 full days in the dryer. However it is essential to test the slices. If the slices are not sufficiently dry, they will become mouldy in a short time. If the slices are not sufficiently dry, the process should be allowed to continue for 1 or 2 hours before checking again.

Can solar drying work for me?

Yes, if you have excess fruit and vegetables that you wish to process and store for later use or if there is a possibility to sell your excess produce in a form that is easier to transport and store. Once your solar dryer has been constructed or bought you are usinq free energy from the sun to preseve your excess food, therefore you don't have to spend any money on nrunning costs connected with the solar dryer.

Solar drying can preserve fruit and vegetables in a very healthy manner, ensuring essential nutrients and vitamins remain in the produce. This is of benefit to ensure that healthy food is available for example to the ill, aged and young children.

In South Africa, some experiments have been carried out with solar dryers in community development projects. Feedback has been very positive in terms of the functionality of the dryers but porjects note that if solar dryers are intended as an income generationa ctivity, additional support and training in terms of marketing the produce is required. Projets are often situated far from markets and transportcan also be an issue.

Benefits of solar drying

1. Surplus food can be dried to avoid waste;
2. It puts food in the cupboand for later use and increases household food security;
3. It can create employment opportunities and a sustainable income;
4. Dried products improve family nutrition because fruit and vegetables contain high quantities of vitamins, minerals and fibre;
5. For diabetics, dried fruit prepared without adding sugar is a healthy choice instead of desserts;
6. Improves the bargaining position of farmers. Sometimes farmers sell at very low prices during the harvest season because they cannot store or preserve their surplus produce;
7. Households are encouraged to establish their own gardens.

Where to find more information on solar drying

In South Africa there are unfortunately no commercially available solar dryers. However, SESSA can put you in contact with pnoducers who can make soler dryers on order or you can dobtain plans to construct your own dryer. For large scale scale commercial applications products are available internationally. For further information please contact SESSA.